FAQ: Lambda Function Code Challenge - Double Or Zero

This community-built FAQ covers the “Double Or Zero” exercise from the lesson “Lambda Function Code Challenge”.

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I receive a syntax error on line 2 when running this:

#Write your lambda function here
double_or_zero = lambda num: num*2 if
num > 10 else 0
print double_or_zero(15)
print double_or_zero(5)

What is wrong with the script?

*edit: Although the example provided in the lesson had a line break where I put mine (after “if”), the issue was that I needed the entire lambda function on one line. Bringing the rest up on line 2 after “if” fixed the error. It’s a bit confusing to include an example with a line break without explaining that.

So I tried:

double_or_zero = lambda num: num * 2 if num > 10 else return 0

and this gave an ‘invalid syntax’ error

after looking at the solution it shows that the ‘return’ statement is unnecessary, so it should look like:

double_or_zero = lambda num: num * 2 if num > 10 else 0

Can someone explain why this is?

The lambda returns one value or the other, implicitly. To illustrate we could use the MAP function…

>>> double_or_zero = lambda num: num * 2 if num > 10 else 0
>>> nums = [5, 10, 15, 20, 16, 12, 8, 4]
>>> map(double_or_zero, nums)
[0, 0, 30, 40, 32, 24, 0, 0]
>>> 
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