Python Assert Quiz
At Europython conference, in my presentation, I talked about re-formulations of Python into simpler Python. It is my intention to turn this into a series of Python quiz questions that you will hopefully enjoy.
Update
Due to comments feedback, I made it more clear that “-O” affects of course both cases, and due to work on getting the recent CPython2.7 test suite to work, I noticed, how the re-formulation for Quiz Question 2 needed a version dependent solution.
And I thought this one was easy. :-)
Quiz Question 1
Say you have the following code:
assert x == y
How can you achieve the same thing, without using the assert
statement at all. The behavior is required to be absolutely the same.
The answer is in the next paragraph, so stop reading if you want to find out yourself.
Solution 1
The correct answer is that assertions are the same as a raise exception in a conditional statement.
if not x == y:
raise AssertionError
The thing where this makes a difference, is “-O”, which will discard assertions, but I consider it rarely used. To be really compatible with that, it should be:
if __debug__ and not x == y:
raise AssertionError
Quiz Question 2
But wait, there is slightly more to it. Say you have the following code:
assert x == y, arg
How can you achieve the same thing, without using the assert
statement at all. The behavior is required to be absolutely the same.
The answer is in the next paragraph, so stop reading if you want to find out yourself.
Solution 2
This is actually version dependent, due to recent optimizations of CPython.
For version 2.6 it is as follows:
The extra value to
assert, simply becomes an extra value to raise, which indicates, delayed creation of theAssertionErrorexception.if not x == y: raise AssertionError, arg
For version 2.7 and higher it is as follows:
The extra value to
assert, simply becomes the argument to creating theAssertionErrorexception.if not x == y: raise AssertionError(arg)
So, even in the more complex case, you end up with a conditional
raise.
The only thing where this makes a difference, is “-O”, which will discard assertions, but I consider it rarely used. To be really compatible with that, it should be:
if __debug__ and not x == y: raise AssertionError ....
Surprised? Well, yes, there really is nothing to assert statements.
I am using this for my Python compiler Nuitka
which benefits from having not to deal with assert as anything
special at all. See also the respective section in the Developer Manual which explains this
and other things.