code: def _find_python(python):
          
          is_pypy = python.startswith("pypy")
  
          # Parse python specifier
          if is_pypy:
              executable = python
              if python == 'pypy':
                  python_version = '2'
              else:
                  python_version = python[4:]
          else:
              python_version = python
              executable = "python{0}".format(python_version)
  
          # Find Python executable on path
          try:
              return util.which(executable)
          except IOError:
              pass
  
          # Maybe the current one is correct?
          current_is_pypy = hasattr(sys, 'pypy_version_info')
          current_versions = ['{0[0]}'.format(sys.version_info),
                              '{0[0]}.{0[1]}'.format(sys.version_info)]
  
          if is_pypy == current_is_pypy and python_version in current_versions:
              return sys.executable
  
          return None
docs: Find Python executable for the given Python version