ctypes

ctypes is a foreign function library for Python that provides C compatible data types and allows calling functions in DLLs or shared libraries. It enables Python code to interface with existing C libraries without writing extension modules. Included in the Python standard library since Python 2.5, ctypes works across platforms by loading dynamic libraries on Windows and POSIX systems.

Its core features include C types such as c_int, c_double, and c_char_p; support for structures and unions via Structure and Union; arrays; and pointers created with POINTER. Libraries are loaded with CDLL or PyDLL on Unix-like systems and with WinDLL or Windll on Windows.

Function prototypes are declared by setting restype and argtypes, which enables proper conversion between Python and C types. The module also provides CFUNCTYPE for creating C-compatible callbacks and supports passing pointers with byref. Error handling includes get_errno/set_errno, and on Windows get_last_error/set_last_error. Memory management is largely automatic, though developers may allocate buffers or manage lifetimes for ctypes objects as needed.

Typical usage involves loading a library, defining needed C types and function prototypes, and calling functions from Python with automatic type conversion. Limitations include the risk of crashes from incorrect prototypes, dependence on platform ABIs, and potential performance overhead relative to native extensions. ctypes is often compared with cffi and SWIG: it is part of the standard library and requires no separate compilation, while cffi can offer broader C coverage and, in some cases, better performance.