def __init__(self, pattern, flags=0):
        """BSON regular expression data.

        This class is useful to store and retrieve regular expressions that are
        incompatible with Python's regular expression dialect.

        :Parameters:
          - `pattern`: string
          - `flags`: (optional) an integer bitmask, or a string of flag
            characters like "im" for IGNORECASE and MULTILINE
        """
        if not isinstance(pattern, (text_type, bytes)):
            raise TypeError("pattern must be a string, not %s" % type(pattern))
        self.pattern = pattern

        if isinstance(flags, string_type):
            self.flags = str_flags_to_int(flags)
        elif isinstance(flags, int):
            self.flags = flags
        else:
            raise TypeError(
                "flags must be a string or int, not %s" % type(flags))
BSON regular expression data.

        This class is useful to store and retrieve regular expressions that are
        incompatible with Python's regular expression dialect.

        :Parameters:
          - `pattern`: string
          - `flags`: (optional) an integer bitmask, or a string of flag
            characters like "im" for IGNORECASE and MULTILINE
        
stackoverflow/venv/lib/python3.6/site-packages/bson/regex.py