pychecker(1) program to check python scripts for common mistakes


pychecker [options] files...


This manual page documents briefly the pychecker command. It was written for the Debian GNU/Linux distribution because the original program does not have a manual page.

pychecker is a program that finds common bugs in python source code. It finds problems that are typically caught by a compiler for less dynamic languages, like C and C++. 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.


By default, the /usr/bin/pychecker script executes pychecker using the default Python interpreter in /usr/bin/python. Some users may want to run pychecker with a different Python interpreter. To accommodate this, the
 /usr/bin/pychecker script supports the use of $PYTHONVER on the command-line, i.e.

PYTHONVER=2.3 pychecker

If $PYTHONVER is set, /usr/bin/pychecker will attempt to execute pychecker using /usr/bin/python$PYTHONVER instead of /usr/bin/python.

Note, however, that this will only work for versions of the python interpreter supported by the current Debian Python infrastructure, not for any arbitrary Python interpreter installed in /usr/bin.


Long options can be preceded with no- to turn off (e.g., no-namedargs). Default settings are indicated by [brackets]

Major Options:

only warn about files passed on the command line [off]
-e, --level
the maximum error level of warnings to be displayed
-#, --limit
the maximum number of warnings to be displayed [10]
-F, --config
specify .pycheckrc file to use
support Quixote's PTL modules
list of evil C extensions that crash the interpreter [[]]

Error Control:

-i, --import
unused imports [on]
-k, --pkgimport
unused imports from [on]
-M, --reimportself
module imports itself [on]
-X, --reimport
reimporting a module [on]
-x, --miximport
module does import and from ... import [on]
-l, --local
unused local variables, except tuples [on]
-t, --tuple
all unused local variables, including tuples [off]
-9, --members
all unused class data members [off]
-v, --var
all unused module variables [off]
-p, --privatevar
unused private module variables [on]
-g, --allglobals
report each occurrence of global warnings [off]
-n, --namedargs
functions called with named arguments (like keywords) [off]
-a, --initattr
Attributes (members) must be defined in __init__() [off]
-I, --initsubclass
Subclass.__init__() not defined [off]
-u, --callinit
Baseclass.__init__() not called [on]
-0, --abstract
Subclass needs to override methods that only throw exceptions [on]
-N, --initreturn
Return None from __init__() [on]
-8, --unreachable
unreachable code [off]
-2, --constCond
a constant is used in a conditional statement [on]
-1, --constant1
1 is used in a conditional statement (if 1: or while 1:) [off]
check if iterating over a string [on]
check improper use of string.find() [on]
-A, --callattr
Calling data members as functions [off]
-y, --classattr
class attribute does not exist [on]
-S, --self
First argument to methods [self]
First argument to classmethods [['cls', 'klass']]
-T, --argsused
unused method/function arguments [on]
-z, --varargsused
unused method/function variable arguments [on]
-G, --selfused
ignore if self is unused in methods [off]
-o, --override
check if overridden methods have the same signature [on]
check if __special__ methods exist and have the correct signature [on]
-U, --reuseattr
check if function/class/method names are reused [on]
-Y, --positive
check if using unary positive (+) which is usually meaningless [on]
-j, --moddefvalue
check if modify (call method) on a parameter that has a default value [on]
check if variables are set to different types [off]
check if unpacking a non-sequence [on]
check if unpacking sequence with the wrong length [on]
check if raising or catching bad exceptions [on]
-4, --noeffect
check if statement appears to have no effect [on]
check if using (expr % 1), it has no effect on integers and strings [on]
check if using (expr is const-literal), doesn't always work on integers and strings [on]

Possible Errors:

-r, --returnvalues
check consistent return values [on]
-C, --implicitreturns
check if using implict and explicit return values [on]
-O, --objattrs
check that attributes of objects exist [on]
-7, --slots
various warnings about incorrect usage of __slots__ [on]
-3, --properties
using properties with classic classes [on]
check if __slots__ is empty [on]
-D, --intdivide
check if using integer division [on]
-w, --shadow
check if local variable shadows a global [on]
-s, --shadowbuiltin
check if a variable shadows a builtin [on]


check if input() is used [on]
-6, --exec
check if the exec statement is used [off]


-q, --stdlib
ignore warnings from files under standard library [off]
-b, --blacklist
ignore warnings from the list of modules [['Tkinter', 'wxPython', 'gtk', 'GTK', 'GDK']]
-Z, --varlist
ignore global variables not used if name is one of these values [['__version__', '__warningregistry__', '__all__', '__credits__', '__test__', '__author__', '__email__', '__revision__', '__id__', '__copyright__', '__license__', '__date__']]
-E, --unusednames
ignore unused locals/arguments if name is one of these values [['_', 'empty', 'unused', 'dummy']]
ignore use of deprecated modules/functions [on]


-L, --maxlines
maximum lines in a function [200]
-B, --maxbranches
maximum branches in a function [50]
-R, --maxreturns
maximum returns in a function [10]
-J, --maxargs
maximum # of arguments to a function [10]
-K, --maxlocals
maximum # of locals in a function [40]
-5, --maxrefs
maximum # of identifier references (Law of Demeter) [5]
-m, --moduledoc
no module doc strings [off]
-c, --classdoc
no class doc strings [off]
-f, --funcdoc
no function/method doc strings [off]


print a .pycheckrc file generated from command line args
-P, --printparse
print internal checker parse structures [off]
-d, --debug
turn on debugging for checker [off]
-Q, --quiet
turn off all output except warnings [off]
-V, --version
print the version of PyChecker and exit


Pychecker was written by Neal Norwitz and Eric C. Newton. Other contributors are listed in /usr/share/doc/pychecker/MAINTAINERS

This manual page was written by Fredrik Steen <[email protected]> for the Debian GNU/Linux system (but may be used by others). It has been subsequently modified by Kenneth J. Pronovici <[email protected]>.