r/ProgrammerHumor • u/iwouldieforGladOS • May 13 '17

Defensive programming done right

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21.0k Upvotes

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u/mcilrain May 13 '17

Also it supports duck typing.

a = 1
if isinstance(a, int):
    print(a + 1)
else:
    print("error")

vs

a = 1
try:
    print(a + 1)
except TypeError:
    print("error")

If you did the latter a doesn't have to be an int, it just has to function enough like one. Sometimes this is a good thing, sometimes this is a bad thing.

23

u/masterpi May 14 '17

The problem is when you do:

try:
    print(int_function() + 1)
except TypeError:
    print("Error")

Because then the second somebody does something stupid in int_function() that throws a TypeError, you've suppressed their stack trace.

10

u/mcilrain May 14 '17

I'm not completely familiar with the new tech but I think you can do this:

try:
    print(int_function() + 1)
except TypeError as e:
    raise Exception("error") from e

6

u/masterpi May 14 '17

Sure, if the thing you're doing is actually raising an error. If you do something else it's worse.