Trying to create assert error not working?

Question

I'm making a very basic code that will check if the list in the dictionary length is greater than the integer in the other key of the dictionary.

For example, if I had:

d = {'lst': [1,2,3,4,5] , 'compare': 5}

Would be fine, because the max number of values (or length) of the list can be 5 (less than or equal to is fine).

This on the other hand should throw an assertion error:

d = {'lst': [1,2,3,4,5,6] , 'compare': 5}

because the length of the list in the key 'lst' > 'compare'.

Here's what I tried:

if len(d['lst']) > d['compare']:
    assert 'Queue is larger than max capacity'
else:
    pass

I'm brand new to using 'assert', so I'm likely using this wrong. If anyone could give me a hand it would be much appreciated!

https://stackoverflow.com/questions/5142418/what-is-the-use-of-assert-in-python — Nitin Pandey, Feb 08 '19 at 19:01
No parentheses are necessary; `assert` is a statement, not a function, so that the expression used for the second argument is only evaluated if the condition evaluates to `False`. — chepner, Feb 08 '19 at 19:04
`assert` will check whether the message string is empty, which it isn't, so it doesn't fail. — Peter Wood, Feb 08 '19 at 19:05

score 1 · Accepted Answer · answered Feb 08 '19 at 19:01

The assert statement takes the condition as the first "argument". No if statement is required.

assert len(d['lst'] <= d['compare']), "Queue is larger than max capacity"

If the condition is false, an AssertionError (which includes the optional second argument) is raised. Otherwise, nothing happens.

Think of assert foo, bar as a shortcut for

# assert foo, bar
if foo:
    raise AssertionError(bar)

1 Answers1