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Exceptions

Exceptions

keywords

• try
• except
• as
• else
• finally

try:
    codeblock
{
[except [ exception-class [ as noun ] ] :
    codeblock
|
except [ ( exception-class-1 , exception-class-2 [, … , exception-class-n] ) [ as noun ] ]
}

examples

Dealing with 1 or multiple exceptions

def divide(n):
    try:
        1/n
        chr(n)
    except (ArithmeticError, ZeroDivisionError):
        print('oops, not a correct mathematical operation')
    except ValueError:
        print('wrong value José: ', n)
    else:
        print('else is only executed in case no exception was caught')
    finally:
        print('finally is always executed')


divide(0)
print('------------------')
divide(-1)
print('------------------')
divide(2)

output

oops, not a correct mathematical operation
finally is always executed
------------------
wrong value José:  -1
finally is always executed
------------------
else is only executed in case no exception was caught
finally is always executed

Exceptions are also classes

You can actually do something with the exception that’s being raised (not thrown for any Java people).
Once you get grip of the Exception class, you can do with it whatever you’d do with any other class cfr python cheat sheet

The magic keyword here is: ‘as’.
try something and except the raised error class as a noun which can be used in the subsequent code

def as_error(text):
    try:
        int(text)
    except ValueError as error:
        print('an error occurred')
        print(error)


as_error('hello')

output

an error occurred
invalid literal for int() with base 10: 'hello'

The BaseException class

The BaseException is a special case of Exception class as this is the parentclass for all other Exception classes

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