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Python 201 -- (Slightly) Advanced Python Topics | |
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Python 201 -- (Slightly) Advanced Python Topics | |
Dave Kuhlman
http://www.rexx.com/~dkuhlman
Email: [email protected]
Release 1.00
June 6, 2003
Copyright (c) 2003 Dave Kuhlman
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
This document is intended as notes for a course on (slightly) advanced Python topics.
Defining a regular expression is to provide a sequence of characters, the pattern, that will match sequences of characters in a target.
Here are several places to look for help:
The patterns or regular expressions can be defined as follows:
\d" (any digit),
"\w" (any
alphanumeric character), "\W" (any non-alphanumeric
character), etc. See
Python Library Reference: 4.2.1 Regular Expression Syntax for more.
Because of the use of backslashes in patterns, you are usually
better off defining regular expressions with raw strings, e.g.
r"abc".
When a regular expression is to be used more than once, you should consider compiling it. For example:
import sys, re
pat = re.compile('aa[bc]*dd')
while 1:
line = raw_input('Enter a line ("q" to quit):')
if line == 'q':
break
if pat.search(line):
print 'matched:', line
else:
print 'no match:', line
Comments:
Use match to match at the beginning of a string (or not at all).
Use search to search a string and match the first string from the left.
Here are some examples:
>>> import re
>>> pat = re.compile('aa[0-9]*bb')
>>> x = pat.match('aa1234bbccddee')
>>> x
<_sre.SRE_Match object at 0x401e9608>
>>> x = pat.match('xxxxaa1234bbccddee')
>>> x
>>> type(x)
<type 'NoneType'>
>>> x = pat.search('xxxxaa1234bbccddee')
>>> x
<_sre.SRE_Match object at 0x401e9608>
Notes:
>>> x = re.search(pat, 'xxxxaa1234bbccddee') >>> x <_sre.SRE_Match object at 0x401e9560>
Match objects enable you to extract matched sub-strings after performing a match. A match object is returned by successful match.
Here is an example:
import sys, re
pat = re.compile('aa([0-9]*)bb')
while 1:
line = raw_input('Enter a line ("q" to quit):')
if line == 'q':
break
mo = pat.search(line)
if mo:
value = mo.group(1)
print 'value: %s' % value
else:
print 'no match'
Explanation:
In addition, you can:
You can extract multiple items with a single search. Here is an example:
import sys, re
pat = re.compile('aa([0-9]*)bb([0-9]*)cc')
while 1:
line = raw_input('Enter a line ("q" to quit):')
if line == 'q':
break
mo = pat.search(line)
if mo:
value1, value2 = mo.group(1, 2)
print 'value1: %s value2: %s' % (value1, value2)
else:
print 'no match'
Comments:
You can locate sub-strings (slices) of a match and replace them. Here is an example:
import sys, re
pat = re.compile('aa([0-9]*)bb([0-9]*)cc')
while 1:
line = raw_input('Enter a line ("q" to quit): ')
if line == 'q':
break
mo = pat.search(line)
if mo:
value1, value2 = mo.group(1, 2)
start1 = mo.start(1)
end1 = mo.end(1)
start2 = mo.start(2)
end2 = mo.end(2)
print 'value1: %s start1: %d end1: %d' % (value1, start1, end1)
print 'value2: %s start2: %d end2: %d' % (value2, start2, end2)
repl1 = raw_input('Enter replacement #1: ')
repl2 = raw_input('Enter replacement #2: ')
newline = line[:start1] + repl1 + line[end1:start2] + repl2 + line[end2:]
print 'newline: %s' % newline
else:
print 'no match'
Explanation:
newline = line[:start1] + repl1 + line[end1:start2] + repl2 + line[end2:]
You can also use the sub function or method to do substitutions. Here is an example:
import sys, re
pat = re.compile('[0-9]+')
print 'Replacing decimal digits.'
while 1:
target = raw_input('Enter a target line ("q" to quit): ')
if target == 'q':
break
repl = raw_input('Enter a replacement: ')
result = pat.sub(repl, target)
print 'result: %s' % result
And, finally, you can define a function to be used to insert calculated replacements. Here is an example:
import sys, re, string
pat = re.compile('[a-m]+')
def replacer(mo):
return string.upper(mo.group(0))
print 'Upper-casing a-m.'
while 1:
target = raw_input('Enter a target line ("q" to quit): ')
if target == 'q':
break
result = pat.sub(replacer, target)
print 'result: %s' % result
Notes:
This is also a convenient use for a lambda instead of a named function, for example:
import sys, re, string
pat = re.compile('[a-m]+')
print 'Upper-casing a-m.'
while 1:
target = raw_input('Enter a target line ("q" to quit): ')
if target == 'q':
break
result = pat.sub(
lambda mo: string.upper(mo.group(0)),
target)
print 'result: %s' % result
Unit test and the Python unit test framework provide a convenient way to define and run tests that ensure that a Python application produces specified results.
This section, while it will not attempt to explain everything about the unit test framework, will provide examples of several straight-forward ways to construct and run tests.
Some assumptions:
class MyTest:
def test_one(self):
# some test code
pass
def test_two(self):
# some test code
pass
# make the test suite.
def suite():
loader = unittest.TestLoader()
testsuite = loader.loadTestsFromTestCase(MyTest)
return testsuite
# Make the test suite; run the tests.
def test():
testsuite = suite()
runner = unittest.TextTestRunner(sys.stdout, verbosity=2)
result = runner.run(testsuite)
Here is a more complete example:
import sys, StringIO, string
import unittest
import webserv_example_heavy_sub
# A comparison function for case-insenstive sorting.
def mycmpfunc(arg1, arg2):
return cmp(string.lower(arg1), string.lower(arg2))
class XmlTest(unittest.TestCase):
def test_import_export1(self):
inFile = file('test1_in.xml', 'r')
inContent = inFile.read()
inFile.close()
doc = webserv_example_heavy_sub.parseString(inContent)
outFile = StringIO.StringIO()
outFile.write('<?xml version="1.0" ?>\n')
doc.export(outFile, 0)
outContent = outFile.getvalue()
outFile.close()
self.failUnless(inContent == outContent)
# make the test suite.
def suite():
loader = unittest.TestLoader()
# Change the test method prefix: test --> trial.
#loader.testMethodPrefix = 'trial'
# Change the comparison function that determines the order of tests.
#loader.sortTestMethodsUsing = mycmpfunc
testsuite = loader.loadTestsFromTestCase(XmlTest)
return testsuite
# Make the test suite; run the tests.
def test_main():
testsuite = suite()
runner = unittest.TextTestRunner(sys.stdout, verbosity=2)
result = runner.run(testsuite)
if __name__ == "__main__":
test_main()
Running the above script produces the following output:
test_import_export (__main__.XmlTest) ... ok ---------------------------------------------------------------------- Ran 1 test in 0.035s OK
A few notes on this example:
loader.testMethodPrefix = 'trial'
loader.sortTestMethodsUsing = mycmpfunc
As a bit of motivation for creating and using unit tests, while developing this example, I discovered several errors (or maybe "special features") in generateDS.py.
Extending vs. embedding -- They are different but related:
Documentation -- The two important sources for information about extending and embedding are the following:
Types of extensions:
Tools -- There are several tools that support the development of Python extensions:
Writing an extension module by hand -- What to do:
Implementing a wrapper function -- What to do:
if (!PyArg_ParseTuple(args, "(ii)(ii)", &x, &y, &width, &height))
{
return NULL;
} /* if */
A sample call might be:
lowerLeft = (x1, y1) extent = (width1, height1) scan(lowerLeft, extent)
if (!PyArg_ParseTuple(args, "O:setContentHandler", &pythonInstance))
{
return NULL;
} /* if */
char * message;
int messageNo;
message = NULL;
messageNo = -1;
/* Is the argument a string?
*/
if (! PyArg_ParseTuple(args, "s", &message))
{
/* It's not a string. Clear the error.
* Then try to get a message number (an integer).
*/
PyErr_Clear();
if (! PyArg_ParseTuple(args, "i", &messageNo))
{
o
o
o
if (n == 0)
{
PyErr_SetString(PyExc_ValueError, "Value must not be zero");
return NULL;
}
See Include/pyerrors.h in the Python source distribution for more exception/error types.
if (PyErr_Occurred())
{
/* An exception was raised.
* Do something about it.
*/
o
o
o
For more documentation on errors and exceptions, see: http://www.python.org/doc/current/api/exceptionHandling.html.
Note: Our discussion and examples are for SWIG version 1.3
SWIG will often enable you to generate wrappers for functions in an existing C function library. SWIG does not understand everything in C header files. But it does a fairly impressive job. You should try it first before resorting to the hard work of writing wrappers by hand.
More information on SWIG is at http://www.swig.org.
Here are some steps that you can follow:
%module MyLibrary
%{
#include "MyLibrary.h"
%}
%include "MyLibrary.h"
Comments:
%module MyLibrary
%{
#include "MyLibrary.h"
%}
int calcArea(int width, int height);
int calcVolume(int radius);
This example will generate wrappers for only two functions.
swig -python MyLibrary.i
gcc -c MyLibrary.c gcc -c -I/usr/local/include/python2.3 MyLibrary_wrap.c gcc -shared MyLibrary.o MyLibrary_wrap.o -o _MyLibrary.so
Note that we produce a shared library whose name is the module name prefixed with an underscore. SWIG also generates a .py file, without the leading underscore, which we will import from our Python code and which, in turn, imports the shared library.
Python 2.3b1 (#1, Apr 25 2003, 20:36:09) [GCC 2.95.4 20011002 (Debian prerelease)] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> import MyLibrary >>> MyLibrary.calcArea(4.0, 5.0) 20.0
Here is a makefile that will execute swig to generate wrappers, then compile and link the extension.
CFLAGS = -I/usr/local/include/python2.3
all: _MyLibrary.so
_MyLibrary.so: MyLibrary.o MyLibrary_wrap.o
gcc -shared MyLibrary.o MyLibrary_wrap.o -o _MyLibrary.so
MyLibrary.o: MyLibrary.c
gcc -c MyLibrary.c -o MyLibrary.o
MyLibrary_wrap.o: MyLibrary_wrap.c
gcc -c ${CFLAGS} MyLibrary_wrap.c -o MyLibrary_wrap.o
MyLibrary_wrap.c: MyLibrary.i
swig -python MyLibrary.i
clean:
rm -f MyLibrary.py MyLibrary.o MyLibrary_wrap.c \
MyLibrary_wrap.o _MyLibrary.so
Here is an example of running this makefile:
$ make -f MyLibrary_makefile clean
rm -f MyLibrary.py MyLibrary.o MyLibrary_wrap.c \
MyLibrary_wrap.o _MyLibrary.so
$ make -f MyLibrary_makefile
gcc -c MyLibrary.c -o MyLibrary.o
swig -python MyLibrary.i
gcc -c -I/usr/local/include/python2.3 MyLibrary_wrap.c -o MyLibrary_wrap.o
gcc -shared MyLibrary.o MyLibrary_wrap.o -o _MyLibrary.so
And, here are C source files that can be used in our example:
/* MyLibrary.h */ float calcArea(float width, float height); float calcVolume(float radius); int getVersion(); int getMode();
/* MyLibrary.c
*/
float calcArea(float width, float height)
{
return (width * height);
}
float calcVolume(float radius)
{
return (3.14 * radius * radius);
}
int getVersion()
{
return 123;
}
int getMode()
{
return 1;
}
Pyrex is a useful tool for writing Python extensions. Because the Pyrex language is similar to Python, writing extensions in Pyrex is easier than doing so in C.
More information on Pyrex is at http://www.cosc.canterbury.ac.nz/~greg/python/Pyrex/.
Here is a simple function definition in Pyrex.
# python_201_pyrex_string.pyx
import string
def formatString(object s1, object s2):
s1 = string.strip(s1)
s2 = string.strip(s2)
s3 = '<<%s||%s>>' % (s1, s2)
s4 = s3 * 4
return s4
And, here is a make file:
CFLAGS = -DNDEBUG -O3 -Wall -Wstrict-prototypes -fPIC \
-I/usr/local/include/python2.3
all: python_201_pyrex_string.so
python_201_pyrex_string.so: python_201_pyrex_string.o
gcc -shared python_201_pyrex_string.o -o python_201_pyrex_string.so
python_201_pyrex_string.o: python_201_pyrex_string.c
gcc -c ${CFLAGS} python_201_pyrex_string.c -o python_201_pyrex_string.o
python_201_pyrex_string.c: python_201_pyrex_string.pyx
pyrexc python_201_pyrex_string.pyx
clean:
rm -f python_201_pyrex_string.so python_201_pyrex_string.o \
python_201_pyrex_string.c
Here is another example. In this one, one function in the .pyx file calls another. Here is the implementation file:
# python_201_pyrex_primes.pyx
def showPrimes(int kmax):
plist = primes(kmax)
for p in plist:
print 'prime: %d' % p
cdef primes(int kmax):
cdef int n, k, i
cdef int p[1000]
result = []
if kmax > 1000:
kmax = 1000
k = 0
n = 2
while k < kmax:
i = 0
while i < k and n % p[i] <> 0:
i = i + 1
if i == k:
p[k] = n
k = k + 1
result.append(n)
n = n + 1
return result
And, here is a make file:
#CFLAGS = -DNDEBUG -g -O3 -Wall -Wstrict-prototypes -fPIC \
# -I/usr/local/include/python2.3
CFLAGS = -DNDEBUG -I/usr/local/include/python2.3
all: python_201_pyrex_primes.so
python_201_pyrex_primes.so: python_201_pyrex_primes.o
gcc -shared python_201_pyrex_primes.o -o python_201_pyrex_primes.so
python_201_pyrex_primes.o: python_201_pyrex_primes.c
gcc -c ${CFLAGS} python_201_pyrex_primes.c -o python_201_pyrex_primes.o
python_201_pyrex_primes.c: python_201_pyrex_primes.pyx
pyrexc python_201_pyrex_primes.pyx
clean:
rm -f python_201_pyrex_primes.so python_201_pyrex_primes.o \
python_201_pyrex_primes.c
Here is the output from running the makefile:
$ make -f python_201_pyrex_makeprimes clean
rm -f python_201_pyrex_primes.so python_201_pyrex_primes.o \
python_201_pyrex_primes.c
$ make -f python_201_pyrex_makeprimes
pyrexc python_201_pyrex_primes.pyx
gcc -c -DNDEBUG -I/usr/local/include/python2.3 python_201_pyrex_primes.c -o python_201_pyrex_primes.o
gcc -shared python_201_pyrex_primes.o -o python_201_pyrex_primes.so
Here is an interactive example of its use:
$ python Python 2.3b1 (#1, Apr 25 2003, 20:36:09) [GCC 2.95.4 20011002 (Debian prerelease)] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> import python_201_pyrex_primes >>> dir(python_201_pyrex_primes) ['__builtins__', '__doc__', '__file__', '__name__', 'showPrimes'] >>> python_201_pyrex_primes.showPrimes(5) prime: 2 prime: 3 prime: 5 prime: 7 prime: 11
This next example shows how to use Pyrex to implement a new extension type, that is a new Python built-in type. Notice that the class is declared with the cdef keyword, which tells Pyrex to generate the C implementation of a type instead of a class.
Here is the implementation file:
# python_201_pyrex_clsprimes.pyx
"""An implementation of primes handling class
for a demonstration of Pyrex.
"""
cdef class Primes:
"""A class containing functions for
handling primes.
"""
def showPrimes(self, int kmax):
"""Show a range of primes.
Use the method primes() to generate the primes.
"""
plist = self.primes(kmax)
for p in plist:
print 'prime: %d' % p
def primes(self, int kmax):
"""Generate the primes in the range 0 - kmax.
"""
cdef int n, k, i
cdef int p[1000]
result = []
if kmax > 1000:
kmax = 1000
k = 0
n = 2
while k < kmax:
i = 0
while i < k and n % p[i] <> 0:
i = i + 1
if i == k:
p[k] = n
k = k + 1
result.append(n)
n = n + 1
return result
And, here is a make file:
CFLAGS = -DNDEBUG -I/usr/local/include/python2.3
all: python_201_pyrex_clsprimes.so
python_201_pyrex_clsprimes.so: python_201_pyrex_clsprimes.o
gcc -shared python_201_pyrex_clsprimes.o -o python_201_pyrex_clsprimes.so
python_201_pyrex_clsprimes.o: python_201_pyrex_clsprimes.c
gcc -c ${CFLAGS} python_201_pyrex_clsprimes.c -o python_201_pyrex_clsprimes.o
python_201_pyrex_clsprimes.c: python_201_pyrex_clsprimes.pyx
pyrexc python_201_pyrex_clsprimes.pyx
clean:
rm -f python_201_pyrex_clsprimes.so python_201_pyrex_clsprimes.o \
python_201_pyrex_clsprimes.c
Here is output from running the makefile:
$ make -f python_201_pyrex_makeclsprimes clean
rm -f python_201_pyrex_clsprimes.so python_201_pyrex_clsprimes.o \
python_201_pyrex_clsprimes.c
$ make -f python_201_pyrex_makeclsprimes
pyrexc python_201_pyrex_clsprimes.pyx
gcc -c -DNDEBUG -I/usr/local/include/python2.3 python_201_pyrex_clsprimes.c -o python_201_pyrex_clsprimes.o
gcc -shared python_201_pyrex_clsprimes.o -o python_201_pyrex_clsprimes.so
And here is an interactive example of its use:
$ python Python 2.3b1 (#1, Apr 25 2003, 20:36:09) [GCC 2.95.4 20011002 (Debian prerelease)] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> import python_201_pyrex_clsprimes >>> dir(python_201_pyrex_clsprimes) ['Primes', '__builtins__', '__doc__', '__file__', '__name__'] >>> primes = python_201_pyrex_clsprimes.Primes() >>> dir(primes) ['__class__', '__delattr__', '__doc__', '__getattribute__', '__hash__', '__init__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__str__', 'primes', 'showPrimes'] >>> primes.showPrimes(4) prime: 2 prime: 3 prime: 5 prime: 7
Documentation -- Also notice that Pyrex preserves the documentation for the module, the class, and the methods in the class. You can show this documentation with pydoc, as follows:
$ pydoc python_201_pyrex_clsprimes
Or, in Python interactive mode, use:
$ python Python 2.3b1 (#1, Apr 25 2003, 20:36:09) [GCC 2.95.4 20011002 (Debian prerelease)] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> import python_201_pyrex_clsprimes >>> help(python_201_pyrex_clsprimes)
Choose SWIG when:
Choose Pyrex when:
The goal -- A new built-in data type for Python.
Existing examples -- Objects/listobject.c, Objects/stringobject.c, Objects/dictobject.c, etc in the Python source code distribution.
In older versions of the Python source code distribution, a template for the C code was provided in Objects/xxobject.c. Objects/xxobject.c is no longer included in the Python source code distribution. However:
And, you can use Pyrex to generate a new built-in type. To do so, implement a Python/Pyrex class and declare the class with the Pyrex keyword cdef. In fact, you may want to use Pyrex to generate a minimal extension type, and then edit that generated code to insert and add functionality by hand. See the Pyrex section for an example.
Pyrex also goes some way toward giving you access to (existing) C structs and functions from Python.
Extension classes the easy way -- SWIG shadow classes.
Start with an implementation of a C++ class and its header file.
Use the following SWIG flags:
swig -c++ -python mymodule.i
More information is available with the SWIG documentation at: http://www.swig.org/Doc1.3/Python.html.
Extension classes the Pyrex way -- An alternatie is to use Pyrex to compile a class definition that does not have the cdef keyword. Using cdef on the class tells Pyrex to generate an extension type instead of a class. You will have to determine whether you want an extension class or an extension type.
Python is an excellent language for text analysis.
In some cases, simply splitting lines of text into words will be enough. In these cases use string.split().
In other cases, regular expressions may be able to do the parsing you need. If so, see the section on regular expressions in this document.
However, in some cases, more complex analysis of input text is required. This section describes some of the ways that Python can help you with this complex parsing and analysis.
There are a number of special purpose parsers which you will find in the Python standard library:
For simple grammars, this is not so hard.
You will need to implement:
Here is an example of a recursive descent parser written in Python. After the example is some explanation.
#!/usr/bin/env python
"""
python_201_rparser.py
A recursive descent parser example.
The grammar:
Prog ::= Command | Command Prog
Command ::= Func_call
Func_call ::= Term '(' Func_call_list ')'
Func_call_list ::= Func_call | Func_call ',' Func_call_list
Term = <word>
"""
import sys, string, types
import getopt
## from IPython.Shell import IPShellEmbed
## ipshell = IPShellEmbed((),
## banner = '>>>>>>>> Into IPython >>>>>>>>',
## exit_msg = '<<<<<<<< Out of IPython <<<<<<<<')
#
# Constants
#
# AST node types
NoneNodeType = 0
ProgNodeType = 1
CommandNodeType = 2
FuncCallNodeType = 3
FuncCallListNodeType = 4
TermNodeType = 5
# Token types
NoneTokType = 0
LParTokType = 1
RParTokType = 2
WordTokType = 3
CommaTokType = 4
EOFTokType = 5
# Dictionary to map node type values to node type names
NodeTypeDict = {
NoneNodeType: 'NoneNodeType',
ProgNodeType: 'ProgNodeType',
CommandNodeType: 'CommandNodeType',
FuncCallNodeType: 'FuncCallNodeType',
FuncCallListNodeType: 'FuncCallListNodeType',
TermNodeType: 'TermNodeType',
}
#
# Representation of a node in the AST (abstract syntax tree).
#
class ASTNode:
def __init__(self, nodeType, *args):
self.nodeType = nodeType
self.children = []
for item in args:
self.children.append(item)
def show(self, level):
self.showLevel(level)
print 'Node -- Type %s' % NodeTypeDict[self.nodeType]
level += 1
for child in self.children:
if isinstance(child, ASTNode):
child.show(level)
elif type(child) == types.ListType:
for item in child:
item.show(level)
else:
self.showLevel(level)
print 'Child:', child
def showLevel(self, level):
for idx in range(level):
print ' ',
#
# The recursive descent parser class.
# Contains the "recognizer" methods, which implement the grammar
# rules (above), one recognizer method for each production rule.
#
class ProgParser:
def __init__(self):
pass
def parseFile(self, infileName):
self.infileName = infileName
self.tokens = None
self.tokenType = NoneTokType
self.token = ''
self.lineNo = -1
self.infile = file(self.infileName, 'r')
self.tokens = genTokens(self.infile)
try:
self.tokenType, self.token, self.lineNo = self.tokens.next()
except StopIteration:
raise RuntimeError, 'Empty file'
result = self.prog_reco()
self.infile.close()
self.infile = None
return result
def parseStream(self, instream):
self.tokens = genTokens(instream, '<instream>')
try:
self.tokenType, self.token, self.lineNo = self.tokens.next()
except StopIteration:
raise RuntimeError, 'Empty file'
result = self.prog_reco()
return result
def prog_reco(self):
commandList = []
while 1:
result = self.command_reco()
if not result:
break
commandList.append(result)
return ASTNode(ProgNodeType, commandList)
def command_reco(self):
if self.tokenType == EOFTokType:
return None
result = self.func_call_reco()
return ASTNode(CommandNodeType, result)
def func_call_reco(self):
if self.tokenType == WordTokType:
term = ASTNode(TermNodeType, self.token)
self.tokenType, self.token, self.lineNo = self.tokens.next()
if self.tokenType == LParTokType:
self.tokenType, self.token, self.lineNo = self.tokens.next()
result = self.func_call_list_reco()
if result:
if self.tokenType == RParTokType:
self.tokenType, self.token, self.lineNo = \
self.tokens.next()
return ASTNode(FuncCallNodeType, term, result)
else:
raise ParseError(self.lineNo, 'missing right paren')
else:
raise ParseError(self.lineNo, 'bad func call list')
else:
raise ParseError(self.lineNo, 'missing left paren')
else:
return None
def func_call_list_reco(self):
terms = []
while 1:
result = self.func_call_reco()
if not result:
break
terms.append(result)
if self.tokenType != CommaTokType:
break
self.tokenType, self.token, self.lineNo = self.tokens.next()
return ASTNode(FuncCallListNodeType, terms)
#
# The parse error exception class.
#
class ParseError(Exception):
def __init__(self, lineNo, msg):
RuntimeError.__init__(self, msg)
self.lineNo = lineNo
self.msg = msg
def getLineNo(self):
return self.lineNo
def getMsg(self):
return self.msg
def is_word(token):
for letter in token:
if letter not in string.ascii_letters:
return None
return 1
#
# Generate the tokens.
# Usage:
# gen = genTokens(infile)
# tokType, tok, lineNo = gen.next()
# ...
def genTokens(infile):
lineNo = 0
while 1:
lineNo += 1
try:
line = infile.next()
except:
yield (EOFTokType, None, lineNo)
toks = line.split()
for tok in toks:
if is_word(tok):
tokType = WordTokType
elif tok == '(':
tokType = LParTokType
elif tok == ')':
tokType = RParTokType
elif tok == ',':
tokType = CommaTokType
yield (tokType, tok, lineNo)
def test(infileName):
parser = ProgParser()
#ipshell('(test) #1\nCtrl-D to exit')
result = None
try:
result = parser.parseFile(infileName)
except ParseError, exp:
sys.stderr.write('ParseError: (%d) %s\n' % \
(exp.getLineNo(), exp.getMsg()))
if result:
result.show(0)
USAGE_TEXT = """
Usage:
python rparser.py [options] <inputfile>
Options:
-h, --help Display this help message.
Example:
python rparser.py myfile.txt
"""
def usage():
print USAGE_TEXT
sys.exit(-1)
def main():
args = sys.argv[1:]
try:
opts, args = getopt.getopt(args, 'h', ['help'])
except:
usage()
relink = 1
for opt, val in opts:
if opt in ('-h', '--help'):
usage()
if len(args) != 1:
usage()
test(args[0])
if __name__ == '__main__':
main()
#import pdb
#pdb.run('main()')
And, here is a sample of the data we can apply this parser to:
aaa ( ) bbb ( ccc ( ) ) ddd ( eee ( ) , fff ( ggg ( ) , hhh ( ) , iii ( ) ) )
Comments and explanation:
Lexical analysis -- The tokenizer in our recursive descent parser example was (for demonstration purposes) overly simple. You can always write more complex tokenizers by hand. However, for more complex (and real) tokenizers, you may want to use a tool to build your tokenizer.
In this section we'll describe Plex and use it to produce a tokenizer for our recursive descent parser.
You can obtain Plex at http://www.cosc.canterbury.ac.nz/~greg/python/Plex/.
In order to use it, you may want to add Plex-1.1.4/Plex to your PYTHONPATH.
Here is a simple example from the Plex tutorial:
#!/usr/bin/env python
# python_201_plex1.py
#
# Sample Plex lexer
#
import sys
import Plex
def test(infileName):
letter = Plex.Range("AZaz")
digit = Plex.Range("09")
name = letter + Plex.Rep(letter | digit)
number = Plex.Rep1(digit)
space = Plex.Any(" \t\n")
comment = Plex.Str('"') + Plex.Rep( Plex.AnyBut('"')) + Plex.Str('"')
resword = Plex.Str("if", "then", "else", "end")
lexicon = Plex.Lexicon([
(resword, 'keyword'),
(name, 'ident'),
(number, 'int'),
( Plex.Any("+-*/=<>"), Plex.TEXT),
(space, Plex.IGNORE),
(comment, 'comment'),
])
infile = open(infileName, "r")
scanner = Plex.Scanner(lexicon, infile, infileName)
while 1:
token = scanner.read()
position = scanner.position()
print '(%d, %d) tok: %s tokType: %s' % \
(position[1], position[2], token[1], token[0])
if token[0] is None:
break
USAGE_TEXT = """
Usage: python python_201_plex1.py <infile>
"""
def usage():
print USAGE_TEXT
sys.exit(-1)
def main():
args = sys.argv[1:]
if len(args) != 1:
usage()
infileName = args[0]
test(infileName)
if __name__ == '__main__':
main()
#import pdb
#pdb.run('main()')
Comments and explanation:
And, here are some comments on constructing the patterns used in a lexicon:
Range constructs a pattern that matches any character
in the range.
Rep constructs a pattern that matches a sequence of
zero or more items.
Rep1 constructs a pattern that matches a sequence of
one or more items.
Any constructs a pattern that matches any one character
in its argument.
Now let's revisit our recursive descent parser, this time with a tokenizer built with Plex. The tokenizer is trivial, but will serve as an example of how to hook it into a parser.
#!/usr/bin/env python
"""
python_201_rparser_plex.py
A recursive descent parser example.
This example uses Plex to implement a tokenizer.
The grammar:
Prog ::= Command | Command Prog
Command ::= Func_call
Func_call ::= Term '(' Func_call_list ')'
Func_call_list ::= Func_call | Func_call ',' Func_call_list
Term = <word>
"""
import sys, string, types
import getopt
import Plex
## from IPython.Shell import IPShellEmbed
## ipshell = IPShellEmbed((),
## banner = '>>>>>>>> Into IPython >>>>>>>>',
## exit_msg = '<<<<<<<< Out of IPython <<<<<<<<')
#
# Constants
#
# AST node types
NoneNodeType = 0
ProgNodeType = 1
CommandNodeType = 2
FuncCallNodeType = 3
FuncCallListNodeType = 4
TermNodeType = 5
# Token types
NoneTokType = 0
LParTokType = 1
RParTokType = 2
WordTokType = 3
CommaTokType = 4
EOFTokType = 5
# Dictionary to map node type values to node type names
NodeTypeDict = {
NoneNodeType: 'NoneNodeType',
ProgNodeType: 'ProgNodeType',
CommandNodeType: 'CommandNodeType',
FuncCallNodeType: 'FuncCallNodeType',
FuncCallListNodeType: 'FuncCallListNodeType',
TermNodeType: 'TermNodeType',
}
#
# Representation of a node in the AST (abstract syntax tree).
#
class ASTNode:
def __init__(self, nodeType, *args):
self.nodeType = nodeType
self.children = []
for item in args:
self.children.append(item)
def show(self, level):
self.showLevel(level)
print 'Node -- Type %s' % NodeTypeDict[self.nodeType]
level += 1
for child in self.children:
if isinstance(child, ASTNode):
child.show(level)
elif type(child) == types.ListType:
for item in child:
item.show(level)
else:
self.showLevel(level)
print 'Child:', child
def showLevel(self, level):
for idx in range(level):
print ' ',
#
# The recursive descent parser class.
# Contains the "recognizer" methods, which implement the grammar
# rules (above), one recognizer method for each production rule.
#
class ProgParser:
def __init__(self):
pass
def parseFile(self, infileName):
self.tokens = None
self.tokenType = NoneTokType
self.token = ''
self.lineNo = -1
self.infile = file(infileName, 'r')
self.tokens = genTokens(self.infile, infileName)
try:
self.tokenType, self.token, self.lineNo = self.tokens.next()
except StopIteration:
raise RuntimeError, 'Empty file'
result = self.prog_reco()
self.infile.close()
self.infile = None
return result
def parseStream(self, instream):
self.tokens = None
self.tokenType = NoneTokType
self.token = ''
self.lineNo = -1
self.tokens = genTokens(self.instream, '<stream>')
try:
self.tokenType, self.token, self.lineNo = self.tokens.next()
except StopIteration:
raise RuntimeError, 'Empty stream'
result = self.prog_reco()
self.infile.close()
self.infile = None
return result
def prog_reco(self):
commandList = []
while 1:
result = self.command_reco()
if not result:
break
commandList.append(result)
return ASTNode(ProgNodeType, commandList)
def command_reco(self):
if self.tokenType == EOFTokType:
return None
result = self.func_call_reco()
return ASTNode(CommandNodeType, result)
def func_call_reco(self):
if self.tokenType == WordTokType:
term = ASTNode(TermNodeType, self.token)
self.tokenType, self.token, self.lineNo = self.tokens.next()
if self.tokenType == LParTokType:
self.tokenType, self.token, self.lineNo = self.tokens.next()
result = self.func_call_list_reco()
if result:
if self.tokenType == RParTokType:
self.tokenType, self.token, self.lineNo = \
self.tokens.next()
return ASTNode(FuncCallNodeType, term, result)
else:
raise ParseError(self.lineNo, 'missing right paren')
else:
raise ParseError(self.lineNo, 'bad func call list')
else:
raise ParseError(self.lineNo, 'missing left paren')
else:
return None
def func_call_list_reco(self):
terms = []
while 1:
result = self.func_call_reco()
if not result:
break
terms.append(result)
if self.tokenType != CommaTokType:
break
self.tokenType, self.token, self.lineNo = self.tokens.next()
return ASTNode(FuncCallListNodeType, terms)
#
# The parse error exception class.
#
class ParseError(Exception):
def __init__(self, lineNo, msg):
RuntimeError.__init__(self, msg)
self.lineNo = lineNo
self.msg = msg
def getLineNo(self):
return self.lineNo
def getMsg(self):
return self.msg
#
# Generate the tokens.
# Usage - example
# gen = genTokens(infile)
# tokType, tok, lineNo = gen.next()
# ...
def genTokens(infile, infileName):
letter = Plex.Range("AZaz")
digit = Plex.Range("09")
name = letter + Plex.Rep(letter | digit)
lpar = Plex.Str('(')
rpar = Plex.Str(')')
comma = Plex.Str(',')
comment = Plex.Str("#") + Plex.Rep(Plex.AnyBut("\n"))
space = Plex.Any(" \t\n")
lexicon = Plex.Lexicon([
(name, 'word'),
(lpar, 'lpar'),
(rpar, 'rpar'),
(comma, 'comma'),
(comment, Plex.IGNORE),
(space, Plex.IGNORE),
])
scanner = Plex.Scanner(lexicon, infile, infileName)
while 1:
tokenType, token = scanner.read()
name, lineNo, columnNo = scanner.position()
if tokenType == None:
tokType = EOFTokType
token = None
elif tokenType == 'word':
tokType = WordTokType
elif tokenType == 'lpar':
tokType = LParTokType
elif tokenType == 'rpar':
tokType = RParTokType
elif tokenType == 'comma':
tokType = CommaTokType
else:
tokType = NoneTokType
tok = token
yield (tokType, tok, lineNo)
def test(infileName):
parser = ProgParser()
#ipshell('(test) #1\nCtrl-D to exit')
result = None
try:
result = parser.parseFile(infileName)
except ParseError, exp:
sys.stderr.write('ParseError: (%d) %s\n' % \
(exp.getLineNo(), exp.getMsg()))
if result:
result.show(0)
USAGE_TEXT = """
Usage:
python python_201_rparser_plex.py [options] <inputfile>
Options:
-h, --help Display this help message.
Example:
python python_201_rparser_plex.py myfile.txt
"""
def usage():
print USAGE_TEXT
sys.exit(-1)
def main():
args = sys.argv[1:]
try:
opts, args = getopt.getopt(args, 'h', ['help'])
except:
usage()
for opt, val in opts:
if opt in ('-h', '--help'):
usage()
if len(args) != 1:
usage()
infileName = args[0]
test(infileName)
if __name__ == '__main__':
main()
#import pdb
#pdb.run('main()')
And, here is a sample of the data we can apply this parser to:
# Test for recursive descent parser and Plex. # Command #1 aaa() # Command #2 bbb (ccc()) # An end of line comment. # Command #3 ddd(eee(), fff(ggg(), hhh(), iii())) # End of test
Comments:
For complex parsing tasks, you may want to consider the following tools:
And, for lexical analysis, you may also want to look at -- Using Regular Expressions for Lexical Analysis.
In this section we will show how to implement our parser example with PLY.
First down-load PLY. It is available at http://systems.cs.uchicago.edu/ply/.
Then add the PLY directory to your PYTHONPATH.
Learn how to construct lexers and parsers with PLY by reading doc/ply.html in the distribution of PLY and by looking at the examples in the distribution.
For those of you who want a more complex example, see A Python Parser for the RELAX NG Compact Syntax, which is implemented with PLY.
Now, here is our example parser. Comments and explanations are below.
#!/usr/bin/env python
"""
python_201_parser_ply.py
A parser example.
This example uses PLY to implement a lexer and parser.
The grammar:
Prog ::= Command*
Command ::= Func_call
Func_call ::= Term '(' Func_call_list ')'
Func_call_list ::= Func_call*
Term = <word>
"""
import sys, types
import getopt
import lex
import yacc
#
# Globals
#
startlinepos = 0
#
# Constants
#
# AST node types
NoneNodeType = 0
ProgNodeType = 1
CommandNodeType = 2
CommandListNodeType = 3
FuncCallNodeType = 4
FuncCallListNodeType = 5
TermNodeType = 6
# Dictionary to map node type values to node type names
NodeTypeDict = {
NoneNodeType: 'NoneNodeType',
ProgNodeType: 'ProgNodeType',
CommandNodeType: 'CommandNodeType',
CommandListNodeType: 'CommandListNodeType',
FuncCallNodeType: 'FuncCallNodeType',
FuncCallListNodeType: 'FuncCallListNodeType',
TermNodeType: 'TermNodeType',
}
#
# Representation of a node in the AST (abstract syntax tree).
#
class ASTNode:
def __init__(self, nodeType, *args):
self.nodeType = nodeType
self.children = []
for item in args:
self.children.append(item)
def append(self, item):
self.children.append(item)
def show(self, level):
self.showLevel(level)
print 'Node -- Type: %s' % NodeTypeDict[self.nodeType]
level += 1
for child in self.children:
if isinstance(child, ASTNode):
child.show(level)
elif type(child) == types.ListType:
for item in child:
item.show(level)
else:
self.showLevel(level)
print 'Value:', child
def showLevel(self, level):
for idx in range(level):
print ' ',
#
# Exception classes
#
class LexerError(Exception):
def __init__(self, msg, lineno, columnno):
self.msg = msg
self.lineno = lineno
self.columnno = columnno
def show(self):
sys.stderr.write('Lexer error (%d, %d) %s\n' % \
(self.lineno, self.columnno, self.msg))
class ParserError(Exception):
def __init__(self, msg, lineno, columnno):
self.msg = msg
self.lineno = lineno
self.columnno = columnno
def show(self):
sys.stderr.write('Parser error (%d, %d) %s\n' % \
(self.lineno, self.columnno, self.msg))
#
# Lexer specification
#
tokens = (
'NAME',
'LPAR','RPAR',
'COMMA',
)
# Tokens
t_LPAR = r'\('
t_RPAR = r'\)'
t_COMMA = r'\,'
t_NAME = r'[a-zA-Z_][a-zA-Z0-9_]*'
# Ignore whitespace
t_ignore = ' \t'
# Ignore comments ('#' to end of line)
def t_COMMENT(t):
r'\#[^\n]*'
pass
def t_newline(t):
r'\n+'
global startlinepos
startlinepos = t.lexer.lexpos - 1
t.lineno += t.value.count("\n")
def t_error(t):
global startlinepos
msg = "Illegal character '%s'" % (t.value[0])
columnno = t.lexer.lexpos - startlinepos
raise LexerError(msg, t.lineno, columnno)
#
# Parser specification
#
def p_prog(t):
'prog : command_list'
t[0] = ASTNode(ProgNodeType, t[1])
def p_command_list_1(t):
'command_list : command'
t[0] = ASTNode(CommandListNodeType, t[1])
def p_command_list_2(t):
'command_list : command_list command'
t[1].append(t[2])
t[0] = t[1]
def p_command(t):
'command : func_call'
t[0] = ASTNode(CommandNodeType, t[1])
def p_func_call_1(t):
'func_call : term LPAR RPAR'
t[0] = ASTNode(FuncCallNodeType, t[1])
def p_func_call_2(t):
'func_call : term LPAR func_call_list RPAR'
t[0] = ASTNode(FuncCallNodeType, t[1], t[3])
def p_func_call_list_1(t):
'func_call_list : func_call'
t[0] = ASTNode(FuncCallListNodeType, t[1])
def p_func_call_list_2(t):
'func_call_list : func_call_list COMMA func_call'
t[1].append(t[3])
t[0] = t[1]
def p_term(t):
'term : NAME'
t[0] = ASTNode(TermNodeType, t[1])
def p_error(t):
global startlinepos
msg = "Syntax error at '%s'" % t.value
columnno = t.lexer.lexpos - startlinepos
raise ParserError(msg, t.lineno, columnno)
#
# Parse the input and display the AST (abstract syntax tree)
#
def parse(infileName):
startlinepos = 0
# Build the lexer
lex.lex(debug=1)
# Build the parser
yacc.yacc()
# Read the input
infile = file(infileName, 'r')
content = infile.read()
infile.close()
try:
# Do the parse
result = yacc.parse(content)
# Display the AST
result.show(0)
except LexerError, exp:
exp.show()
except ParserError, exp:
exp.show()
USAGE_TEXT = """
Usage:
python python_201_parser_ply.py [options] <inputfile>
Options:
-h, --help Display this help message.
Example:
python python_201_parser_ply.py testfile.prog
"""
def usage():
print USAGE_TEXT
sys.exit(-1)
def main():
args = sys.argv[1:]
try:
opts, args = getopt.getopt(args, 'h', ['help'])
except:
usage()
relink = 1
for opt, val in opts:
if opt in ('-h', '--help'):
usage()
if len(args) != 1:
usage()
infileName = args[0]
parse(infileName)
if __name__ == '__main__':
main()
#import pdb
#pdb.run('main()')
Applying this parser to the following input:
# Test for recursive descent parser and Plex. # Command #1 aaa() # Command #2 bbb (ccc()) # An end of line comment. # Command #3 ddd(eee(), fff(ggg(), hhh(), iii())) # End of test
produces the following output:
Node -- Type: ProgNodeType
Node -- Type: CommandListNodeType
Node -- Type: CommandNodeType
Node -- Type: FuncCallNodeType
Node -- Type: TermNodeType
Value: aaa
Node -- Type: CommandNodeType
Node -- Type: FuncCallNodeType
Node -- Type: TermNodeType
Value: bbb
Node -- Type: FuncCallListNodeType
Node -- Type: FuncCallNodeType
Node -- Type: TermNodeType
Value: ccc
Node -- Type: CommandNodeType
Node -- Type: FuncCallNodeType
Node -- Type: TermNodeType
Value: ddd
Node -- Type: FuncCallListNodeType
Node -- Type: FuncCallNodeType
Node -- Type: TermNodeType
Value: eee
Node -- Type: FuncCallNodeType
Node -- Type: TermNodeType
Value: fff
Node -- Type: FuncCallListNodeType
Node -- Type: FuncCallNodeType
Node -- Type: TermNodeType
Value: ggg
Node -- Type: FuncCallNodeType
Node -- Type: TermNodeType
Value: hhh
Node -- Type: FuncCallNodeType
Node -- Type: TermNodeType
Value: iii
Comments and explanation:
t[0]. A deviation from this is
the processing of sequences, discussed below.
except: clauses on the try: statement in
function parse). And, we use an instance of the
exception class as a container in order to "bubble up" information
about the error (e.g. a message, a line number, and a column
number).
pyparsing is a relatively new parsing package for Python. It was implemented and is supported by Paul McGuire and it shows promise. It appears especially easy to use and seems especially appropriate in particular for quick parsing tasks, although it has features that make some complex parsing tasks easy. It follows a very natural Python style for constructing parsers.
Good documentation comes with the pyparsing distribution. See file HowToUseParsing.html. So, I won't try to repeat that here. What follows is an attempt to provide several quick examples to help you solve simple parsing tasks as quickly as possible.
You will also want to look at the samples in the examples directory, which are very helpful. My examples below are fairly simple. You can see more of the ability of pyparsing to handle complex tasks in the examples.
Where to get it - You can find pyparsing at: http://pyparsing.sourceforge.net/.
How to install it - Put the pyparsing module somewhere on your PYTHONPATH.
And now, here are a few examples.
Here is a simple grammar for lines containing fields separated by commas:
import sys
from pyparsing import alphanums, ZeroOrMore, Word
fieldDef = Word(alphanums)
lineDef = fieldDef + ZeroOrMore("," + fieldDef)
args = sys.argv[1:]
if len(args) != 1:
print 'usage: python pyparsing_test1.py <datafile.txt>'
sys.exit(-1)
infilename = sys.argv[1]
infile = file(infilename, 'r')
for line in infile:
fields = lineDef.parseString(line)
print fields
Notes and explanation:
lineDef = fieldDef + ZeroOrMore("," + fieldDef)
with:
lineDef = delimitedList(fieldDef)
And note that delimitedList takes an optional argument delim used to specify the delimiter. The default is a comma.
This example parses expressions of the form ``func(arg1, arg2, arg3)''.
from pyparsing import Word, alphas, alphanums, nums, ZeroOrMore, Literal
lparen = Literal("(")
rparen = Literal(")")
identifier = Word(alphas, alphanums + "_")
integer = Word( nums )
functor = identifier
arg = identifier | integer
args = arg + ZeroOrMore("," + arg)
expression = functor + lparen + args + rparen
content = raw_input("Enter an expression: ")
parsedContent = expression.parseString(content)
print parsedContent
Explanation:
Word("0123456789") as analogous to a regexp containing
the pattern "[0-9]+".
This example parses expressions having the following form:
Input format: [name] [phone] [city, state zip] Last, first 111-222-3333 city, ca 99999
Here is the parser:
import sys
from pyparsing import alphas, nums, ZeroOrMore, Word, Group, Suppress, Combine
lastname = Word(alphas)
firstname = Word(alphas)
city = Group(Word(alphas) + ZeroOrMore(Word(alphas)))
state = Word(alphas, exact=2)
zip = Word(nums, exact=5)
name = Group(lastname + Suppress(",") + firstname)
phone = Combine(Word(nums, exact=3) + "-" + Word(nums, exact=3) + "-" + Word(nums, exact=4))
location = Group(city + Suppress(",") + state + zip)
record = name + phone + location
args = sys.argv[1:]
if len(args) != 1:
print 'usage: python pyparsing_test3.py <datafile.txt>'
sys.exit(-1)
infilename = sys.argv[1]
infile = file(infilename, 'r')
for line in infile:
line = line.strip()
if line and line[0] != "#":
fields = record.parseString(line)
print fields
And, here is some sample input:
Jabberer, Jerry 111-222-3333 Bakersfield, CA 95111 Kackler, Kerry 111-222-3334 Fresno, CA 95112 Louderdale, Larry 111-222-3335 Los Angeles, CA 94001
Here is output from parsing the above input:
[['Jabberer', 'Jerry'], '111-222-3333', [['Bakersfield'], 'CA', '95111']] [['Kackler', 'Kerry'], '111-222-3334', [['Fresno'], 'CA', '95112']] [['Louderdale', 'Larry'], '111-222-3335', [['Los', 'Angeles'], 'CA', '94001']]
Comments:
This example (thanks to Paul McGuire) parses a more complex structure and produces a dictionary.
Here is the code:
from pyparsing import Literal, Word, Group, Dict, ZeroOrMore, alphas, nums,\
delimitedList
import pprint
testData = """
+-------+------+------+------+------+------+------+------+------+
| | A1 | B1 | C1 | D1 | A2 | B2 | C2 | D2 |
+=======+======+======+======+======+======+======+======+======+
| min | 7 | 43 | 7 | 15 | 82 | 98 | 1 | 37 |
| max | 11 | 52 | 10 | 17 | 85 | 112 | 4 | 39 |
| ave | 9 | 47 | 8 | 16 | 84 | 106 | 3 | 38 |
| sdev | 1 | 3 | 1 | 1 | 1 | 3 | 1 | 1 |
+-------+------+------+------+------+------+------+------+------+
"""
# Define grammar for datatable
heading = (Literal(
"+-------+------+------+------+------+------+------+------+------+") +
"| | A1 | B1 | C1 | D1 | A2 | B2 | C2 | D2 |" +
"+=======+======+======+======+======+======+======+======+======+").suppress()
vert = Literal("|").suppress()
number = Word(nums)
rowData = Group( vert + Word(alphas) + vert + delimitedList(number,"|") +
vert )
trailing = Literal(
"+-------+------+------+------+------+------+------+------+------+").suppress()
datatable = heading + Dict( ZeroOrMore(rowData) ) + trailing
# Now parse data and print results
data = datatable.parseString(testData)
print "data:", data
print "data.asList():",
pprint.pprint(data.asList())
print "data keys:", data.keys()
print "data['min']:", data['min']
print "data.max:", data.max
Notes:
print statements show how to get at the items in the
dictionary.
This section will help you to put a GUI (graphical user interface) in your Python program.
We will use a particular GUI library: PyGTK. We've chosen this because it is reasonably light-weight and our goal is to embed light-weight GUI interfaces in an (possibly) existing application.
For simpler GUI needs, consider EasyGUI, which is also described below.
For more heavy-weight GUI needs (for example, complete GUI applications), you may want to explore WxPython. See the WxPython home page at: http://www.wxpython.org/
Information about PyGTK is at:
In this section we explain how to pop up a simple dialog box from your Python application.
To do this, do the following:
Here is a sample that displays a message box:
#!/usr/bin/env python
import sys
import getopt
import gtk
class MessageBox(gtk.Dialog):
def __init__(self, message="", buttons=(), pixmap=None,
modal= gtk.TRUE):
gtk.Dialog.__init__(self)
self.connect("destroy", self.quit)
self.connect("delete_event", self.quit)
if modal:
self.set_modal(gtk.TRUE)
hbox = gtk.HBox(spacing=5)
hbox.set_border_width(5)
self.vbox.pack_start(hbox)
hbox.show()
if pixmap:
self.realize()
pixmap = Pixmap(self, pixmap)
hbox.pack_start(pixmap, expand=gtk.FALSE)
pixmap.show()
label = gtk.Label(message)
hbox.pack_start(label)
label.show()
for text in buttons:
b = gtk.Button(text)
b.set_flags(gtk.CAN_DEFAULT)
b.set_data("user_data", text)
b.connect("clicked", self.click)
self.action_area.pack_start(b)
b.show()
self.ret = None
def quit(self, *args):
self.hide()
self.destroy()
gtk.mainquit()
def click(self, button):
self.ret = button.get_data("user_data")
self.quit()
# create a message box, and return which button was pressed
def message_box(title="Message Box", message="", buttons=(), pixmap=None,
modal= gtk.TRUE):
win = MessageBox(message, buttons, pixmap=pixmap, modal=modal)
win.set_title(title)
win.show()
gtk.mainloop()
return win.ret
def test():
result = message_box(title='Test #1',
message='Here is your message',
buttons=('Ok', 'Cancel'))
print 'result:', result
USAGE_TEXT = """
Usage:
python simple_dialog.py [options]
Options:
-h, --help Display this help message.
Example:
python simple_dialog.py
"""
def usage():
print USAGE_TEXT
sys.exit(-1)
def main():
args = sys.argv[1:]
try:
opts, args = getopt.getopt(args, 'h', ['help'])
except:
usage()
relink = 1
for opt, val in opts:
if opt in ('-h', '--help'):
usage()
if len(args) != 0:
usage()
test()
if __name__ == '__main__':
main()
#import pdb
#pdb.run('main()')
Some explanation:
And, here is an example that displays an text input dialog:
#!/usr/bin/env python
import sys
import getopt
import gtk
class EntryDialog( gtk.Dialog):
def __init__(self, message="", default_text='', modal= gtk.TRUE):
gtk.Dialog.__init__(self)
self.connect("destroy", self.quit)
self.connect("delete_event", self.quit)
if modal:
self.set_modal(gtk.TRUE)
box = gtk.VBox(spacing=10)
box.set_border_width(10)
self.vbox.pack_start(box)
box.show()
if message:
label = gtk.Label(message)
box.pack_start(label)
label.show()
self.entry = gtk.Entry()
self.entry.set_text(default_text)
box.pack_start(self.entry)
self.entry.show()
self.entry.grab_focus()
button = gtk.Button("OK")
button.connect("clicked", self.click)
button.set_flags(gtk.CAN_DEFAULT)
self.action_area.pack_start(button)
button.show()
button.grab_default()
button = gtk.Button("Cancel")
button.connect("clicked", self.quit)
button.set_flags(gtk.CAN_DEFAULT)
self.action_area.pack_start(button)
button.show()
self.ret = None
def quit(self, w=None, event=None):
self.hide()
self.destroy()
gtk.mainquit()
def click(self, button):
self.ret = self.entry.get_text()
self.quit()
def input_box(title="Input Box", message="", default_text='',
modal= gtk.TRUE):
win = EntryDialog(message, default_text, modal=modal)
win.set_title(title)
win.show()
gtk.mainloop()
return win.ret
def test():
result = input_box(title='Test #2',
message='Enter a valuexxx:',
default_text='a default value')
if result is None:
print 'Canceled'
else:
print 'result: "%s"' % result
USAGE_TEXT = """
Usage:
python simple_dialog.py [options]
Options:
-h, --help Display this help message.
Example:
python simple_dialog.py
"""
def usage():
print USAGE_TEXT
sys.exit(-1)
def main():
args = sys.argv[1:]
try:
opts, args = getopt.getopt(args, 'h', ['help'])
except:
usage()
relink = 1
for opt, val in opts:
if opt in ('-h', '--help'):
usage()
if len(args) != 0:
usage()
test()
if __name__ == '__main__':
main()
#import pdb
#pdb.run('main()')
Most of the explanation for the message box example is relevant to this example, too. Here are some differences:
This example shows a file selection dialog box:
#!/usr/bin/env python
import sys
import getopt
import gtk
class FileChooser(gtk.FileSelection):
def __init__(self, modal=gtk.TRUE, multiple=gtk.TRUE):
gtk.FileSelection.__init__(self)
self.multiple = multiple
self.connect("destroy", self.quit)
self.connect("delete_event", self.quit)
if modal:
self.set_modal(gtk.TRUE)
self.cancel_button.connect('clicked', self.quit)
self.ok_button.connect('clicked', self.ok_cb)
if multiple:
self.set_select_multiple(gtk.TRUE)
## self.hide_fileop_buttons()
self.ret = None
def quit(self, *args):
self.hide()
self.destroy()
gtk.mainquit()
def ok_cb(self, b):
if self.multiple:
self.ret = self.get_selections()
else:
self.ret = self.get_filename()
self.quit()
def file_sel_box(title="Browse", modal=gtk.FALSE, multiple=gtk.TRUE):
win = FileChooser(modal=modal, multiple=multiple)
win.set_title(title)
win.show()
gtk.mainloop()
return win.ret
def file_open_box(modal=gtk.TRUE):
return file_sel_box("Open", modal=modal, multiple=gtk.TRUE)
def file_save_box(modal=gtk.TRUE):
return file_sel_box("Save As", modal=modal, multiple=gtk.FALSE)
def test():
result = file_open_box()
print 'open result:', result
result = file_save_box()
print 'save result:', result
USAGE_TEXT = """
Usage:
python simple_dialog.py [options]
Options:
-h, --help Display this help message.
Example:
python simple_dialog.py
"""
def usage():
print USAGE_TEXT
sys.exit(-1)
def main():
args = sys.argv[1:]
try:
opts, args = getopt.getopt(args, 'h', ['help'])
except:
usage()
relink = 1
for opt, val in opts:
if opt in ('-h', '--help'):
usage()
if len(args) != 0:
usage()
test()
if __name__ == '__main__':
main()
#import pdb
#pdb.run('main()')
A little guidance:
Note that there are also predefined dialogs for font selection (FontSelectionDialog) and color selection (ColorSelectionDialog)
If your GUI needs are minimalist and your application is imperative rather than event driven, then you may want to consider EasyGUI. As the name suggests, it is extremely easy to use.
How to know when you might be able to use EasyGUI:
EasyGUI is available at http://www.ferg.org/easygui/.
Information about EasyGUI is provided in a text file in the distribution.
EasyGUI provides functions for a variety of commonly needed dialog boxes, including:
Here is a simple example that prompts the user for an entry, then shows the response in a message box:
def testeasygui():
response = easygui.enterbox(message='Enter your name:',
title='Name Entry')
easygui.msgbox(message=response,
title='Your Response',
)
Python has an excellent range of implementation organization structures. These range from statements and control structures (at a low level) through functions, methods, and classes (at an intermediate level) and modules and packages at an upper level.
This section provides some guidance with the use of packages. In particular:
A Python package is a collection of Python modules in a disk directory.
In order to be able to import individual modules from a directory, the directory must contain a file named __init__.py. (Note that requirement does not apply to directories that on listed in PYTHONPATH.) The __init__.py serves several purposes:
One simple way to enable the user to import and use a package is to instruct the use to import individual modules from the package.
A second, slightly more advanced way to enable the user to import the package is to expose those features of the package in the __init__ module. Suppose that module mod1 contains functions fun1a and fun1b and suppose that module mod2 contains functions fun2a and fun2b. Then file __init__.py might contain the following:
from mod1 import fun1a, fun1b from mod2 import fun2a, fun2b
Then, if the following is evaluated in the user's code:
import testpackages
Then testpackages will contain fun1a, fun1b, fun2a, and fun2b.
For example, here is an interactive session that demostrates importing the package:
>>> import testpackages >>> print dir(testpackages) [`__builtins__', `__doc__', `__file__', `__name__', `__path__', `fun1a', `fun1b', `fun2a', `fun2b', `mod1', `mod2']
Distutils (Python Distribution Utilities) has special support for distrubuting and installing packages.
In this section we'll learn how to use Distutils to package and install a distribution that contains a single package with multiple modules.
As our example, imagine that we have a directory containing the following:
Notice the sub-directory Testpackages/testpackages containing the file __init__.py. This is the Python package that we will install.
We'll describe how to configure the above files so that they can be packaged as a single distribution file and so that the Python package they contain can be installed as a package by Distutils.
The MANIFEST.in file lists the files that we want included in our distribution. Here is the contents of our MANIFEST.in file:
include README MANIFEST MANIFEST.in include setup.py include testpackages/*.py
The setup.py describes to Distutils (1) how to package the distribution file and (2) how to install the distribution. Here is the contents of our sample setup.py:
#!/usr/bin/env python
from distutils.core import setup # [1]
long_description = 'Tests for installing and distributing Python packages'
setup(name = 'testpackages', # [2]
version = '1.0a',
description = 'Tests for Python packages',
maintainer = 'Dave Kuhlman',
maintainer_email = '[email protected]',
url = 'http://www.rexx.com/ dkuhlman',
long_description = long_description,
packages = ['testpackages'] # [3]
)
Explanation:
Now, to create a distribution file, we run the following:
python setup.py sdist --formats=gztar
which will create a file testpackages-1.0a.tar.gz under the directory dist.
Then, the user, who wishes to install this file, can do so by executing the following:
tar xvzf testpackages-1.0a.tar.gz cd testpackages-1.0a python setup.py build python setup.py install # as root
Thanks to the implementors of Python for producing an exceptionally usable and enjoyable programming language.
Thanks to Dave Beazley and others for SWIG and PLY.
Thanks to Greg Ewing for Pyrex and Plex.
Thanks to James Henstridge for PyGTK.
See Also:
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Python 201 -- (Slightly) Advanced Python Topics | |