try, return and finally – what takes precendence?
Yes, finally-clauses are executed before functions return, but be careful with placing a return-statement inside the finally-caluse!
I encountered some code with a structure like this one at work today:
def divide_numbers_a(a, b):
try:
return a / b
except ZeroDivisionError:
print("Bad stuff happened!")
finally:
print("Close database connection or something like that…")
return None
On one hand, the return statement should make the function exit early when no errors are encoutered, but on the other hand, the code in the finally-clause should always run – which value will be returned?
If the function indeed returns within the try-block, and the except-block is only reached when an exception is thrown and interceptet, is the finally-block reached when an exception in not raised?
def divide_numbers_b(a, b):
try:
return a / b
except ZeroDivisionError:
print("Bad stuff happened!")
finally:
print("Close database connection or something like that…")
return None
Let's try and see what happens!
print(f'{divide_numbers_a(1, 1)=}', end='\n'*2)
print(f'{divide_numbers_a(1, 0)=}', end='\n'*2)
print(f'{divide_numbers_b(1, 1)=}', end='\n'*2)
print(f'{divide_numbers_b(1, 0)=}', end='\n'*2)
So apparently finally-block are executed before the function returns, and including a return-statement there will cause return-statement in the try-block to be bypassed.
But placing a return statement at the end of the function definition and outside the try-except-finally block will still work for returning a default value, since it will only be reached if no other return-statements are executed.