Module wx.tools.dbg

This module provides a useful debugging framework that supports showing nesting of function calls and allows a program to contain lots of debugging print statements that can easily be turned on or off to debug the code. It also supports the ability to have each function indent the debugging statements contained within it, including those of any other function called within its scope, thus allowing you to see in what order functions are being called, and from where.

This capability is particularly useful in wxPython applications, where exactly events occur that cause functions to be called is not entirely clear, and because wxPython programs can't be run from inside other debugging environments that have their own message loops.

This module defines a Logger class, responsible for managing debugging output. Each Logger instance can be given a name at construction; if this is done, '<name>:' will precede each logging output made by that Logger instance.

The log() function this class provides takes a set of positional arguments that are printed in order if debugging is enabled (just like print does), followed by a set of keyword arguments that control the behavior of the log() function itself on subsequent calls. The current keyword arguments are:

indent

When set to a value of 1, this increments the current indentation level, causing all subsequent dbg() outputs to be indented by 3 more spaces. When set to a value of 0, this process is reversed, causing the indent to decrease by 3 spaces. The default indentation level is 0.

enable

When set to a value of 1, this turns on dbg() output for for program importing this module, until told to do otherwise. When set to a value of 0, dbg output is turned off. (dbg output is off by default.)

suspend

When set to a value of 1, this increments the current "suspension" level. This makes it possible for a function to temporarily suspend its and any of its dependents' potential outputs that use the same Logger instance. When set to a value of 0, the suspension level is decremented. When the value goes back to 0, potential logging is resumed (actual output depends on the "enable" status of the Logger instance in question.)

wxlog

When set to a value of 1, the output will be sent to the active wxLog target.

stream

When set to a non-None value, the current output stream (default of sys.stdout) is pushed onto a stack of streams, and is replaced in the dbg system with the specified stream. When called with a value of None, the previous stream will be restored (if stacked.) If set to None without previously changing it will result in no action being taken.

You can also call the log function implicitly on the Logger instance, ie. you can type:

from wxPython.tools.dbg import Logger
dbg = Logger()
dbg('something to print')

Using this fairly simple mechanism, it is possible to get fairly useful debugging output in a program. Consider the following code example:

>>> d = {1:'a', 2:'dictionary', 3:'of', 4:'words'}
>>> dbg = dbg.Logger('module')
>>> dbg(enable=1)
module: dbg enabled
>>> def foo(d):
...     dbg('foo', indent=1)
...     bar(d)
...     dbg('end of foo', indent=0)
...
>>> def bar(d):
...     dbg('bar', indent=1)
...     dbg('contents of d:', indent=1)
...     l = d.items()
...     l.sort()
...     for key, value in l:
...         dbg('%d =' % key, value)
...     dbg(indent=0)
...     dbg('end of bar', indent=0)
...
>>> foo(d)
module: foo
   module: bar
      module: contents of d:
         module: 1 = a
         module: 2 = dictionary
         module: 3 = of
         module: 4 = words
      module: end of bar
   module: end of foo
>>>