docs: def requires(module, name=""):
      """Enforces module presence.
  
      The general use here is to allow conditional imports that may fail (e.g., a
      required python package is not installed) but still allow the rest of the
      python package to compile and run fine. If the wrapped method with this
      decorated is invoked, then a runtime error is generated.
  
      :param module: required module (set as variable to ``None`` on import fail)
      :type  module: ``module`` or ``None``
      :param name: module name
      :type  name: ``string``
      """
      def wrapped(method):
          """Call and enforce method."""
          if module is None:
              raise ImproperlyConfigured("Module '%s' is not installed." % name)
          return method
  
      return wrapped