Exact value from function via AST visitor

test.py

import ast
from collections import namedtuple
import inspect

class ExtractValue(ast.NodeVisitor):
    def __init__(self, func, *, call=None, keyword=None):
        self.source = inspect.getsource(func)
        self.call = call
        self.keyword = keyword

    def extract(self):
        return self.visit(ast.parse(self.source))

    def visit_Call(self, node):
        def get_key(n):
            return n.arg
        def get_value(n):
            if type(n.value) == ast.Num:
                return str(n.value.n)
            else:
                raise

        if node.func.id != self.call:
            return

        # Check if a call or object
        if type(node.args[0]) == ast.Call:
            call = node.args[0]
            split_source = self.source.split('\n')
            line_source = split_source[call.lineno-1][call.col_offset-1+1:]
            # find index after first paren
            index = line_source.find('(') + 1
            # find matching paren
            depth = 1
            while depth > 0:
                if line_source[index] == '(':
                    depth += 1
                elif line_source[index] == ')':
                    depth -= 1
                index += 1

            self.value = eval("{}.{}".format(line_source[:index], self.keyword))

def extract_value(func, *, call=None, keyword=None):
    v = ExtractValue(func, call=call, keyword=keyword)
    return v.extract()

Test = namedtuple('Test', field_names='max')

def test():
    return get_max(Test(max=2))

print(extract_value(test, call='get_max', keyword='max'))