python - mypy "invalid type" error -

i'm trying implement type annotations in current project, , receiving errors mypy don't understand.

i'm using python 2.7.11, , newly installed mypy in base virtualenv. following program runs fine:

from __future__ import print_function types import stringtypes typing import list, union, callable  def f(value):     # type: (stringtypes) -> stringtypes     return value  if __name__ == '__main__':     print("{}".format(f('some text')))     print("{}".format(f(u'some unicode text'))) 

but running mypy --py2 -s mypy_issue.py returns following:

mypy_issue.py: note: in function "f": mypy_issue.py:8: error: invalid type "types.stringtypes" 

the above types appear in typeshed... mypy documentation says "mypy incorporates typeshed project, contains library stubs python builtins , standard library. "... not sure "incorporates" means - need "activate", or provide path to, typeshed? need download , install(?) typeshed locally?

the problem types.stringtypes defined sequence of types -- formal type signature on typeshed is:

stringtypes = (stringtype, unicodetype) 

this corresponds official documentation, states stringtypes constant "a sequence containing stringtype , unicodetype"...

so then, explains error you're getting -- stringtypes isn't actual class (it's tuple) , mypy doesn't recognize valid type.

there several possible fixes this.

the first way use typing.anystr defined anystr = typevar('anystr', bytes, unicode). although anystr included within typing module, is, unfortunately, poorly documented of -- can find more detailed information within mypy docs.

a less cleaner way of expression do:

from types import stringtype, unicodetype typing import union  mystringtypes = union[stringtype, unicodetype]  def f(value):          # type: (mystringtypes) -> mystringtypes     return value 

this works, less desirable because return type no longer obligated same thing input type not want when working different kinds of strings.

and typeshed -- it's bundled default when install mypy. in ideal world, shouldn't need worry typeshed @ all, since mypy in beta , typeshed being updated account missing modules or incorrect type annotations, might worth installing mypy directly github repo , installing typeshed locally if find running bugs typeshed.