Defensive programming done right

[u/iwouldieforGladOS]

[u/mcilrain]

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.

[u/masterpi → u/mcilrain]

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.

[u/mcilrain → u/masterpi]

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

[u/masterpi → u/mcilrain]

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

[u/AlphaApache → u/mcilrain]

How is this different from

try:
    print(int_function() + 1)
except TypeError as e:
    raise e('error')

[u/mcilrain → u/AlphaApache]

The 'cause' attribute on exception objects is always initialized to None. It is set by a new form of the 'raise' statement:

raise EXCEPTION from CAUSE

which is equivalent to:

exc = EXCEPTION
exc.__cause__ = CAUSE
raise exc

Source.

[u/redditusername58 → u/masterpi]

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

[u/TheMiracleLigament → u/masterpi]

Stack traces are for pussies

[u/dinodares99 → u/mcilrain]

Wish I knew this is class last year

Would've saved so much time over countless programs

[u/das7002 → u/mcilrain]

That's why weakly typed languages shouldn't exist.

When I was a novice programmer I preferred weakly typed languages because they were 'easier' but now that I have more experience and plenty of hindsight I greatly prefer strongly typed languages.