1.4.4. Exceptions

Even if a program syntax is correct, there might be issues that occur at runtime. To prevent the program from crashing Python provides a way to handle exceptions.

1.4.4.1. Handling Exceptions

The basic form of exception handling is as follow:

try:
    pass
except SomeException:
    pass
...
except Exception as e:
    pass

In this example we try to execute something. In case it goes wrong, an exception while be raised.
The except statement let us capture the exception for us to handle. We can optionally use the as statement, giving access of the exception instance within the except section.

Each except statement will be will try to match the exception type in order.
The Exception class acts as a wild card to catch (almost) everything.

try:
    1/0
except ZeroDivisionError:
    print("[ERROR] Impossible to divide by 0.")
except Exception as e:
    pass

[ERROR] Impossible to divide by 0.

1.4.4.2. Raising Exceptions

The raise statement force an exception to occur.

try:
    raise TypeError("Wrong type")
except OSError:
    print("OSError occurred")
except TypeError:
    print("TypeError occurred")
except Exception:
    print("Exception occurred")

TypeError occurred

1.4.4.3. Clean-Up Actions

After handling an exception, we might need to have some clean-up action. For example, to release some resources.
The finally statement can be used after the except statements and is always executed, regardless of an error occurring or not.

try:
    raise Exception
except:
    print("Handling Exception")
finally:
    print("Clean-up action")

Handling Exception
Clean-up action