
PyChecker is a tool for finding bugs in python source code.
It finds problems that are typically caught by a compiler for less
dynamic languages, like C and C++.  It is similar to lint.
Because of the dynamic nature of python, some warnings
may be incorrect; however, spurious warnings should be fairly infrequent.

PyChecker works in a combination of ways.  First, it imports each
module.  If there is an import error, the module cannot be processed.
The import provides some basic information about the module.  The code
for each function, class, and method is checked for possible problems.

Types of problems that can be found include:

  * No global found (e.g., using a module without importing it)
  * Passing the wrong number of parameters to functions/methods/constructors
  * Passing the wrong number of parameters to builtin functions & methods
  * Using format strings that don't match arguments
  * Using class methods and attributes that don't exist
  * Changing signature when overriding a method
  * Redefining a function/class/method in the same scope
  * Using a variable before setting it
  * self not the first parameter to a method
  * Unused globals and locals (module or variable)
  * Unused function/method arguments (can ignore self)
  * No doc strings in modules, classes, functions, and methods

Using PyChecker
---------------
To use PyChecker, pass the python source files you want to check
on the command line:

	pychecker file1.py file2.py ...

Note:  On Windows, use pychecker.bat.  You may also need to add
python/scripts to your PATH.

pychecker and pychecker.bat will only exist if pychecker has been
installed.  To install, do:  python setup.py install

Note:  If you haven't installed pychecker, it can be run by doing:
python pychecker/checker.py

An alternate way to use PyChecker is to import it in your code.
See 'Importing PyChecker' below for more details.

If there are import dependencies in your source files, you should
import those files first on the command line in order to get as many
files checked as possible.

PyChecker works with Python 2.0 through 2.3.
Some features don't work on earlier versions of Python.
I only regularly test with versions 2.2 and 2.3.

You can use the test files as examples:

	pychecker [options] test_input/*.py

If you want to change the default behaviour, you can pass command line options
or define a .pycheckrc file.  For an example, look at pycheckrc.

To show the available options, do:

	pychecker -h

Some of the most common options are:

      --only         only warn about files passed on the command line [off]
  -#, --limit        the maximum number of warnings to be displayed [10]
  -s, --shadowbuiltin check if a variable shadows a builtin [on]
  -q, --stdlib       ignore warnings from files under standard library [off]
  -T, --argsused     unused method/function arguments [on]

There is a simple GUI which is not maintained much.  It is good
for showing all the options and also allows you to run pychecker.
To run options, you will need to start it manually:

	python pychecker/options.py

If you want to suppress warnings on a module/function/class/method,
you can define a suppressions dictionary in .pycheckrc.
Examples of keys are:  'module', 'module.function',
		       'module.class', 'module.class.method', etc.

You can also define suppressions in your code by doing:

	__pychecker__ = 'no-namedargs maxreturns=0 unusednames=foo,bar'

The format for __pychecker__ values and values in the suppressions dictionary
are the same.  Dashes (--) are optional when preceding long option names.

Importing PyChecker
-------------------
You can import PyChecker in your code's main module, by doing:

        import pychecker.checker

This will allow each module imported after PyChecker to be checked 
(other than the main module).  NOTE:  Modules imported before PyChecker
will not be checked.  Warnings will be displayed on stdout 
(ie, PyChecker uses print).

Since you can't pass command line parameters, you can do:

        os.environ['PYCHECKER'] = 'command line options here'

This is equivalent of setting PYCHECKER in the shell environment:

        PYCHECKER='no-namedargs maxreturns=0' /path/to/your/program

If you want to disable the warnings (and processing done by PyChecker), 
prior to importing PyChecker, do:

        os.environ['PYCHECKER_DISABLED'] = 1

This is equivalent of setting PYCHECKER_DISABLED in the shell environment:

        PYCHECKER_DISABLED=1 /path/to/your/program

Internal Errors
---------------
If you find a bug in PyChecker, meaning you see something like:

	pychecker myfile.py

	myfile.py:13 INTERNAL ERROR -- STOPPED PROCESSING FUNCTION --
        Traceback (most recent call last):
          File "./pychecker/warn.py", line 364, in _checkFunction
            stack, oparg, lastLineNum)
          File "./pychecker/warn.py", line 195, in _handleFunctionCall
            kwArgs.append(stack[i].data)
        IndexError: list index out of range

Please post a bug in the SourceForge Tracker
(https://sourceforge.net/tracker/?atid=382217&group_id=24686&func=browse)
or send mail indicating the version of PyChecker, *your source file*
which broke PyChecker (myfile.py in the example above), and the traceback.
It is very helpful to provide a simple test case to demonstrate the problem.
It helps to have the entire file and all the dependencies if you cannot
produce a simple test case.  But if you can't provide a test case nor
the file(s), I may be able to figure out the problem with just the line
which broke PyChecker (myfile.py:13 in the example above).

Good Luck!  As always, feedback is greatly appreciated.

Neal
pychecker-list@lists.sourceforge.net

PyChecker can be found on SourceForge at:
	http://pychecker.sourceforge.net/
	http://sourceforge.net/projects/pychecker