spy on variable in python

spy-variable.py

# https://stackoverflow.com/a/34620310/1733117

import sys
import dis
import random

watchme = 123

def foo():
    global watchme
    watchme = 122


def wait_for_changes():
    curr_val = watchme
    def tracefn(frame, event, arg):
        global watchme
        global changed_frame
        if event == 'call':
            frame.f_trace_opcodes = True
        if watchme != curr_val:
            changed_frame = frame
            if event == 'opcode':
                opcode = frame.f_code.co_code[frame.f_lasti]
                opname = dis.opname[opcode]
                print(f"XXX value changed to {watchme} in frame {frame} by opcode {opname}")
            watchme = curr_val
        return tracefn
    sys.settrace(tracefn)

for i in range(100):
    exec(f"""
def foo_{i}():
    global watchme
    watchme = {i}
""")

wait_for_changes()

def random_call():
    n = random.randint(0, 99)
    exec(f"foo_{n}()")

random_call()
random_call()
random_call()