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Dive into python and / or fail

I am stuck in this particular example from immersion in python

Example 4.18. When and / or Trick Fails

>>>>a = ""
>>>>b = "second"
>>>1 and a or b
>>>>'second'

Since a is an empty string that Python considers false in a boolean context, 1 and "evalutes to", and then '' or 'second' evalutes to 'second'. Unfortunately! This is not what you wanted. E-trick, bool and a or b will not work as an expression of C bool? a: b when a is false in the boolean context.

Why does he say that this is not what the user wants, I mean 1, and "will evaluate the value to False, and" "or" b "will evaluate to the" second ", which is fine, what should happen, I don’t I understand why this is wrong? Am I missing something?

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expr if cond else expr inline Python 2.5 PEP 308;

if cond:
    expr
else:
    expr

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condition and a or b a ("", ), (1) true, 1 and a False, b.

The solution to this problem is to either use Python 2.5+ ( if-true if condition else if-false) syntax or make sure that it is if-truenever false. One way to perform the second - pack if-trueand if-falsein a tuple or a list, as a non-empty iterabel always always:

>>> a = ""
>>> b = "second"
>>> condition = 1
>>> condition and a or b
'second'

>>> condition and [a] or [b]
['']

>>> (condition and [a] or [b])[0]
''

This is a kind of ugly solution, but it is there if you need to orient old versions of Python.

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