pycapi 0.1.0

Python bindings to the CPython C API.

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PyCAPI is still in an early development stage. It is incomplete, and may contain some bugs in the interface between the Python and C layers. If so, please report them here!

When you use pycapi functions, you are using the actual underlying API endpoints. Just as when calling them in C or ctypes, there is enormous potential to break things if you don't know what you're doing!

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PyCAPI 0.1.0

PyCAPI is a Python package containing bindings to the CPython C API. Its goal is to support as much of the Python 3.5 - 3.8 stable public APIs as possible.

To install, just run:

$ pip install pycapi

Where is the documentation?

Documentation of the full CPython C API can be found here. It's not a goal of this project to maintain a separate API reference.

Any type conversions (such as Python int with C int, Python bytes with C char*, or Python None with C NULL) should be obvious, and all other semantics (such as refcounts, etc.) are identical to the documented API behavior. For simplicity, PyCAPI doesn't provide any additional functionality or utilities beyond CPython's documented stable public API.

How is PyCAPI better than ctypes.pythonapi?

It's easier to use.

pythonapi implicity requires users to specify the argument and return types as ctypes types:

>>> import ctypes
>>> ctypes.pythonapi.PyNumber_Add(1, 2)
Segmentation fault: 11

>>> import ctypes
>>> ctypes.pythonapi.PyNumber_Add.argtypes = (ctypes.py_object, ctypes.py_object)
>>> ctypes.pythonapi.PyNumber_Add.restype = ctypes.py_object
>>> ctypes.pythonapi.PyNumber_Add(1, 2)
3

It's more complete.

Because pythonapi is based on a DLL, it doesn't offer any APIs that are implemented as macros:

>>> ctypes.pythonapi.PyDict_Check(ctypes.py_object(d))
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "/usr/local/Cellar/python/3.7.2_1/Frameworks/Python.framework/Versions/3.7/lib/python3.7/ctypes/__init__.py", line 369, in __getattr__
    func = self.__getitem__(name)
File "/usr/local/Cellar/python/3.7.2_1/Frameworks/Python.framework/Versions/3.7/lib/python3.7/ctypes/__init__.py", line 374, in __getitem__
    func = self._FuncPtr((name_or_ordinal, self))
AttributeError: dlsym(RTLD_DEFAULT, PyDict_Check): symbol not found

pycapi also fully loaded on import, so you can use tab-completion and other introspection techniques to discover APIs. pythonapi requires you to access the attribute before it is loaded, and there is no way to get a complete listing of what it supports.