stack_tracer.py

# stack_tracer.py
    # before every line of code runs, get stack frames and call render.py
    # user presses Enter to move to run next line of code (otherwise execution is too fast)

import sys
import os
import types
import io
from time import sleep
from render import update_ui

stdout_buffer = io.StringIO()

user_program = ""
comprehensive_flag = False  # if True: can see import module & functions in <module>'s frame's LOCALs

def start_tracing(path_to_user_program, comprehensive):
    global user_program # need global keyword to assign to global var
    user_program = path_to_user_program
    global comprehensive_flag 
    comprehensive_flag = comprehensive
    sys.stdout = stdout_buffer # redirect stdout into our buffer
    sys.settrace(trace) # trace gets called before every line of code runs

def stop_tracing():
    sys.settrace(None)
    sys.stdout = sys.__stdout__ 

# event = "line" / "call" / "return" / "exception"
# 1 frame = 1 function call
def trace(curr_frame, event, arg):
    filename = os.path.abspath(curr_frame.f_code.co_filename)
    if filename != user_program:
        return trace
    if event == "line": # when a line is about to execute (we care about this)
        # print_stack(curr_frame)
        update_ui(curr_frame, stdout_buf=stdout_buffer.getvalue())
        input() # click Enter to step through code line by line
    # elif event == "call":
    #     print(f"\n>>> CALL {curr_frame.f_code.co_name}()")
    #     print_local_vars(curr_frame)
    # elif event == "return":
    #     print(f"\n<<< RETURN {curr_frame.f_code.co_name}() = {arg}")

    return trace    # return itself to keep using this when next event hits