A small wrapper around lib2to3 to help write Python3 compatible code.
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Latest commit 6f4aeff May 1, 2014



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py3kwarn detects code that is not Python 3 compatible. It provides flake8-style warning messages.

See also:

Pull requests are welcome!


Supports Python 2.6, 2.7, and 3.3+

$ pip install py3kwarn

...or to install from the git repository:

$ pip install -e git+git://github.com/liamcurry/py3kwarn.git#egg=py3kwarn

Usage with vim

You can use py3kwarn with syntastic. If you want to use py3kwarn with another syntax checker (like flake8), then you will have to add this to your vim config:

let g:syntastic_python_checkers=['flake8', 'py3kwarn']

Usage from the command line

$ py3kwarn example.py
example.py:2:1: PY3K (FixApply) apply(hello, args, kwargs) -> hello(*args, **kwargs)
example.py:5:1: PY3K (FixBasestring) basestring -> str
example.py:15:1: PY3K (FixDict) d.iteritems(); -> iter(d.items());
example.py:16:1: PY3K (FixDict) d.viewvalues(); -> d.values();
example.py:19:1: PY3K (FixExcept) try:import asdf;except E, T:pass; -> try:import asdf;except E as T:pass;
example.py:25:1: PY3K (FixExec) exec code in ns1, ns2; -> exec(code, ns1, ns2);
example.py:28:1: PY3K (FixExecfile) execfile('test.py') -> exec(compile(open('test.py').read(), 'test.py', 'exec'))
example.py:31:1: PY3K (FixFilter) filter(lambda x: x, [1, 2, 3]) -> [x for x in [1, 2, 3] if x]
example.py:36:1: PY3K (FixFuncattrs) test.func_name; -> test.__name__;
example.py:37:1: PY3K (FixFuncattrs) test.func_closure; -> test.__closure__;
example.py:38:1: PY3K (FixFuncattrs) test.func_dict; -> test.__dict__;
example.py:44:1: PY3K (FixHasKey) d.has_key('foobar') -> 'foobar' in d
example.py:56:1: PY3K (FixInput) input('FixInput') -> eval(input('FixInput'))
example.py:66:1: PY3K (FixItertoolsImports) from itertools import imap ->
example.py:67:1: PY3K (FixItertoolsImports) from itertools import ifilter; ->
example.py:68:1: PY3K (FixItertoolsImports) from itertools import izip; ->
example.py:69:1: PY3K (FixItertoolsImports) from itertools import ifilterfalse; -> from itertools import filterfalse;
example.py:62:1: PY3K (FixLong) long; -> int;
example.py:75:1: PY3K (FixLong) long -> int
example.py:50:1: PY3K (FixImports) import StringIO -> import io
example.py:51:1: PY3K (FixImports) import cStringIO; -> import io;
example.py:52:1: PY3K (FixImports) import cPickle; -> import pickle;
example.py:53:1: PY3K (FixImports) import __builtin__; -> import builtins;
example.py:62:1: PY3K (FixIsinstance) isinstance(x, (int, int)) -> isinstance(x, int)
example.py:63:1: PY3K (FixIsinstance) isinstance(x, (int, int)); -> isinstance(x, int);
example.py:11:1: PY3K (FixCallable) callable('hello') -> isinstance('hello', collections.Callable)
example.py:59:1: PY3K (FixIntern) intern(s) -> sys.intern(s)

Modifying code automatically

Problems can be fixed via py3kwarn2to3:

$ py3kwarn2to3 --write example.py


Testing can be done with make test. py3kwarn also supports tox. This enables quickly testing changes in many versions of python. Take a look at the tox.ini file for more details.


To contribute, fork the repo and clone to your local machine.

Create a virtual environment and

pip install -r requirements_dev.txt

Then just make a pull request with the issues you've fixed!


  • Friendlier messages.
  • A flake8 extension.
  • Flags to ignore certain errors
  • Make it faster. Right now it is quite slow compared to other syntax checkers. Major refactoring may be necessary.