IfStatementWithValue

Legacy Wiki Page

This page was migrated from the old MoinMoin-based wiki. Information may be outdated or no longer applicable. For current documentation, see python.org.

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).