code: def check_source(source_name):
      """Chooses C or pyx source files, and raises if C is needed but missing"""
      source_ext = ".pyx"
      if not HAS_CYTHON:
          source_name = source_name.replace(".pyx.in", ".c")
          source_name = source_name.replace(".pyx", ".c")
          source_ext = ".c"
          if not os.path.exists(source_name):
              msg = (
                  "C source not found.  You must have Cython installed to "
                  "build if the C source files have not been generated."
              )
              raise OSError(msg)
      return source_name, source_ext
  
imports: from setuptools import Command, Extension, find_packages, setup
  from setuptools.dist import Distribution
  from packaging.version import parse
  from collections import defaultdict
  import fnmatch
  import inspect
  import os
  from os.path import dirname, join, relpath
  from pathlib import Path
  import shutil
  import sys
label_desc: Use image node_id 2 for calling a global function with example usage: check_source(source_name) and returns: source_name,  source_ext