get the lists of functions used/called within a function in python

Question

Is there any tool/library through which the list of methods/functions called within another methods/functions can be listed?

For example: If that tool or library runs for below method

def calculate(a: int, b: int, operator: Operator):
    if operator == Operator.add:
        add(a, b)
    elif operator == Operator.subtract
        subtract(a, b)

then it should return

1. add
2. subtract

This question is almost same as this one but it's for Java.

This is basically same as what PyCharm does for Find Usage. Thanks!

Answer 1

This seems to do the work:

import dis
def list_func_calls(fn):
    funcs = []
    bytecode = dis.Bytecode(fn)
    instrs = list(reversed([instr for instr in bytecode]))
    for (ix, instr) in enumerate(instrs):
        if instr.opname=="CALL_FUNCTION":
            load_func_instr = instrs[ix + instr.arg + 1]
            funcs.append(load_func_instr.argval)

    return ["%d. %s" % (ix, funcname) for (ix, funcname) in enumerate(reversed(funcs), 1)]

Example:

>>> list_func_calls(calculate)
['1. add', '2. subtract']

What's happening here is:

1. we make a Bytecode object of the function
2. we reverse the list of instructions, since the function name will follow the function call

3. we step through the list, and for each CALL_FUNCTION instruction,

4. we use the instructions arg parameter to tell us how many arguments we're getting

5. we look one past that to find the instruction that loads the function we're calling

6. we add that function's name (instr.argval) to a list which we then reverse, enumerate, and return in the requested format

Note that since Python 3.6, there are three CALL_FUNCTION instructions, so you'll have to check the documentation to extend this example to be fully functional with current python