List comprehension with if statement

python if-statement list-comprehension
OrangeTux picture OrangeTux · Mar 18, 2013 · Viewed 161.5k times · Source

I want to compare 2 iterables and print the items which appear in both iterables.

>>> a = ('q', 'r')
>>> b = ('q')


# Iterate over a. If y not in b, print y.
# I want to see ['r'] printed.
>>> print([ y if y not in b for y in a])
                              ^

But it gives me a invalid syntax error where the ^ has been placed. What is wrong about this lamba function?

Answer

Volatility picture Volatility · Mar 18, 2013

You got the order wrong. The if should be after the for (unless it is in an if-else ternary operator)

[y for y in a if y not in b]

This would work however:

[y if y not in b else other_value for y in a]

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