Typeshed models function types for the Python standard library and Python builtins, as well as third party packages.

This data can e.g. be used for static analysis, type checking or type inference.

Each Python module is represented by a .pyi "stub". This is a normal Python file (i.e., it can be interpreted by Python 3), except all the methods are empty. Python function annotations (PEP 3107) are used to describe the types the function has. See PEP 484 for the exact syntax of the stub files.

The below is an excerpt from the types for the datetime module.

MAXYEAR = ...  # type: int
MINYEAR = ...  # type: int
__doc__ = ...  # type: str
__file__ = ...  # type: str
__name__ = ...  # type: str
__package__ = ...  # type: None

class date(object):
    def __init__(self, year: int, month: int, day: int) -> None: ...
    @classmethod
    def fromtimestamp(cls, timestamp: int or float) -> date: ...
    @classmethod
    def fromordinal(cls, ordinal: int) -> date: ...
    @classmethod
    def today(self) -> date: ...
    def ctime(self) -> str: ...
    def weekday(self) -> int: ...

This contains stubs for modules the Python standard library -- which includes pure Python modules, dynamically loaded extension modules, hard-linked extension modules, and the builtins.

Modules that are not shipped with Python but have a type description in Python go into third_party. Since these modules can behave differently for different versions of Python, third_party has version subdirectories, just like stdlib.

We're welcoming contributions (pull requests) for type definitions of third party packages.

We store stubs for both Python 2 as well as Python 3. We also distinguish between minor versions (E.g. 3.2 <-> 3.3). To accomplish not having to duplicate modules that are the same between all minor versions, we have e.g. a top-level directory 3/ that contains all the stubs for Python 3. More specialized stubs go into e.g. 3.3/ and supersede the more generic stubs in 3/. Modules that are the same under both Python 2 and Python 3 go into 2and3/. Note that the only supported version of Python 2 is 2.7.

According to PEP 484, type checkers are expected to understand simple version and platform checks. So the following syntax is legal in a pyi:

if sys.version_info[0] >= 3:
    # Python 3 specific definitions
else:
    # Python 2 specific definitions

This can be used for modules in 2and3/ that only have minor changes between Python 2 and Python 3. If the difference between versions is more drastic, it can make more sense to have seperate files in 2.x/ and 3.x/.