Catching exceptions

Learn to catch exceptions in __exit__.

Catching exceptions in a context manager

The __exit__ method can catch errors inside the block. If it returns True the error is suppressed:

class Koruyucu:
    def __enter__(self):
        return self
    def __exit__(self, exc_type, exc_val, exc_tb):
        if exc_type is not None:
            print("hata yakalandı")
            return True

with Koruyucu():
    raise ValueError("test")
# hata yakalandı

Here raise ValueError is raised inside the with block. __exit__ detects it via exc_type and suppresses it by returning True. The program does not crash.

This is useful for temporary error suppression.

Difference between return True and False

If __exit__ returns True the error does not propagate outside the with block — as if it were caught. If it returns False or None the error propagates normally:

# True: error suppressed
# False/None: error propagates

This is similar to an except block in try/except. But in a context manager the suppression is done inside __exit__.

Use carefully — hiding unexpected errors is dangerous.

Exercise Suppress an error with Koruyucu

Define class Koruyucu:. In __enter__ write return self. In __exit__ write if exc_type is not None: print("hata yakalandı"); return True. Inside a with Koruyucu(): block write raise ValueError("test").

Show example solution

class Koruyucu:
    def __enter__(self):
        return self
    def __exit__(self, exc_type, exc_val, exc_tb):
        if exc_type is not None:
            print("hata yakalandı")
            return True

with Koruyucu():
    raise ValueError("test")

Test yourself

What does exc_type being None in __exit__ mean?
- An error occurred
- No error occurred
- The program crashed
- The error was suppressed
Show answer

No error occurred — If exc_type is None there was no error in the block.
Match exception catching

exc_type

Error type
exc_val

Error value
return True

Suppress error
return None

Propagate error

Complete the __exit__ signature

def __exit__(self, ____, exc_val, exc_tb):

Show answer

def __exit__(self, exc_type, exc_val, exc_tb):

Next lesson: ExitStack

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