code: def set_implementation(impl):
      
      global __impl__
      if impl.lower() == 'python':
          __impl__ = __IMPL_PYTHON__
      elif impl.lower() == 'c':
          __impl__ = __IMPL_C__
      else:
          import warnings
          warnings.warn('Implementation '+impl+' is not known. Using the fallback python implementation.')
          __impl__ = __IMPL_PYTHON__
docs: Sets the implementation of this module
  
      Parameters
      ----------
      impl : str
          One of ["python", "c"]