Alternatively, we could use this cheap hack:

/*[python input]
class hidden_object_converter(object_converter):
    show_in_signature = False

[python start generated code]*/

/*[clinic input]
module _sre
class _sre.SRE_Pattern "PatternObject *" "&Pattern_Type"

_sre.SRE_Pattern.match as pattern_match

    string: object
    pos: Py_ssize_t = 0
    endpos: Py_ssize_t(c_default="PY_SSIZE_T_MAX") = sys.maxsize
    pattern: hidden_object = None

...