Wandering Thoughts archives

Finding the name of your caller in Python

One of the things that would be useful in an access tracer is reporting not just what was accessed, but where it was accessed from. A basic starter for this is knowing what function called you.

CPython has enough introspection faculties to give you this information, but it's not entirely documented how to dig it out. The big tool for this is the inspect module, and we can use it to define a function:

import inspect

def getcallerinfo():
    fr = inspect.currentframe()
    try: 
        fr = fr.f_back.f_back
        if fr is None:
            return "<no caller>"
        fi = inspect.getframeinfo(fr, 0)
        if fi[2] == "<module>":
            return "(%s:%d)" % (fi[0], fi[1])
        else:
            return "%s() (%s:%d)" % (fi[2],
                                     fi[0], fi[1])
    finally:
        del fr

This returns something like 'barfunc() (foo.py:30)', which means that the function that called getcallerinfo() was called by barfunc(), specifically the code at line 30 of foo.py.

Technically we don't need to call inspect.getframeinfo() to obtain this information (we could just use fr.f_code.co_filename and so on directly, since they're documented), but it handles some peculiar magic with the file name for us.

(Needless to say, this is probably specific to CPython; I would be surprised if the same code worked in Jython or IronPython or the like. Since all of this is documented, it is at least likely to be portable across different versions of CPython and to keep working in future ones.)