.PYX File Extension
What is a PYX file?
Source code file written in Pyrex, a Python-like language used for writing Python extension modules with C-like syntax; may contain references to existing C modules; compiles code that increases the execution time of Python programs.
Since Pyrex is used for writing modules for Python software, PYX files may sometimes be found with Python applications.
NOTE: Cython is an extension of Pyrex that contains several enhancements, and it is often preferred to Pyrex.