Question

Is it possible to get the function name from a operator.methodcaller in Python?

import operator as op
mc = op.methodcaller('foo')
print magic(mc) #should print 'foo'

How do I do the magic to get the name of the method which methodcaller is calling?

Answer 1

It is, but you need to dig into the C internals (not a recommended solution):

from ctypes import *

PyObject_HEAD = [
    ("ob_refcnt", c_size_t),
    ("ob_type", c_void_p),
]

class methodcallerobject(Structure):
    _fields_ = PyObject_HEAD + [
        ("name", c_void_p),
        ("args", c_void_p),
        ("kwds", c_void_p),
    ]

def magic(methcallobj):
    if not isinstance(methcallobj, operator.methodcaller):
        raise TypeError("not a methodcaller")

    c_methcallobj = cast(c_void_p(id(methcallobj)), POINTER(methodcallerobject)).contents

    return cast(c_methcallobj.name, py_object).value

Note that this only works on CPython and is not particularly beautiful. But if this is the only solution available, it’s better than nothing.