CODEWITHSUNDEEP
pythonpython-3.x
my_question
my_question

Reputation: 3245

How can I add a descriptive string to assert

I like to see some meaningful description at assertion failure.

Here is my code and its execution:

>cat /tmp/1.py
a="aaa" + "bbb"
print(a)
assert ("hello" + a) and 0

>python /tmp/1.py
aaabbb
Traceback (most recent call last):
  File "/tmp/1.py", line 3, in <module>
    assert ("hello" + a) and 0
AssertionError

I am using Python 3.7.

You know why "hello" + a is not evaluated first as a string concatenation? And how can I make it?

Upvotes: 2

Views: 1488

Answers (2)

Carcigenicate
Carcigenicate

Reputation: 45826

According to the docs, the failure message follows a comma:

assert some_condition, "This is the assert failure message".

This is equivalent to:

if __debug__:
    if not some_condition:
        raise AssertionError("This is the assert failure message")

And as noted in the comments, assert is not a function call. Don't add parenthesis, or you may have odd results. assert(condition, message) will be interpreted as a tuple being used as a condition with no message, and will never fail.

Upvotes: 7

Shi XiuFeng
Shi XiuFeng

Reputation: 735

You can add your description just after your assert statement with a comma.

Such as:

assert ("hello" + a) and 0, 'Your description'

The result will be:

aaabbb
Traceback (most recent call last):
  File "test.py", line 6, in <module>
    assert ("hello" + a) and 0, "Your description"
AssertionError: Your description

Upvotes: 2

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