为什么Python中的装饰风格的上下文管理器无法在Tkinter窗口中捕获异常？

Question

there is a simple code with decorator-generated context manager via contextlib. When I press button exception raised and DOES NOT handled by context manager. Why is it?

from Tkinter import Tk, Button
from contextlib import contextmanager


def close_window(): 
    window.destroy()
    raise Exception


@contextmanager
def safe():
    try:
        yield
    except:
        print 'Exception catched'

with safe():
    window = Tk()
    button = Button(window, text='Press me', command=close_window)
    button.pack()
    window.mainloop()

Why does exception still raise?

UPD I use Python 2.7

Answer 1

The Tkinter main process loop is not brought down by exceptions and does not propagate them further. Hence, the exception never reaches till the with statement (since tkinter itself catches and reports the exception and then stops execution).

You will need to create a decorator to catch those exception and log them or do whatever logic you want to do.

Example -

from Tkinter import Tk, Button
from contextlib import contextmanager

class exceptioncatcher: # <---the decorator
    def __init__(self, function):
        self.function = function
    def __call__(self, *args, **kwargs):
        try:
            return self.function(*args, **kwargs)
        except Exception:
            print 'Exception catched1'


@exceptioncatcher
def close_window(): 
    window.destroy()
    raise Exception


@contextmanager
def safe():
    try:
        yield
    except Exception:
        print 'Exception catched'

with safe():
    window = Tk()
    button = Button(window, text='Press me', command=close_window)
    button.pack()
    window.mainloop()

With the above code, when I click on the Press button, it logs Exception catched1 for me and exits.

Also, It is not good to do except: you should give the exception you want to catch (or atleast except Exception: ).