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← Revision 5 as of 2009-03-30 21:57:55 ⇥
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| [[TableOfContents]] | <<TableOfContents>> |
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| See also SwitchStatement | = Accepted Solution = |
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| = Current Python Idioms = | This is now part of Python 2.5: |
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| There are a few ways in Python do achieve the evaluation only of the statement used when the predicate is true: | {{{ A if predicate else B }}} |
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| which would convert the above snippet to: | |
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| {{{ x = sin(cos(x)) if test else cos(sin(x)) }}} |
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| = Proposed Solutions = | = Discussion = |
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| = If always returns a value = {{{ x = if test: A() else: B() }}} |
Please see http://python.org/peps/pep-0308.html and google for discussions about the ternary operator (if you haven't yet). |
Contents
The Problem
Python is sorely missing an if statement that:
- computes and takes the value of A if and only if the predicate is true
- computes and takes the value of B if and only if the predicate is false
In C and its derivitives,
predicate ? A : B
This is extremely useful in programming and helps avoid copy and paste assignments. This is an example of poor code, because the assignment logic "x=" is copied and pasted, violating the software maintainbility and readability principle of OnceAndOnlyOnce:
if test: x=sin(cos(x)) else: x=cos(sin(x))
Accepted Solution
This is now part of Python 2.5:
A if predicate else B
which would convert the above snippet to:
x = sin(cos(x)) if test else cos(sin(x))
Discussion
Please see http://python.org/peps/pep-0308.html and google for discussions about the ternary operator (if you haven't yet).