Why doesn't print work in a lambda?

python printing lambda python-2.x
Anycorn picture Anycorn · Jun 4, 2010 · Viewed 78k times · Source

Why doesn't this work?

lambda: print "x"

Is this not a single statement, or is it something else? The documentation seems a little sparse on what is allowed in a lambda...

Answer

L̲̳o̲̳̳n̲̳̳g̲̳̳p̲̳o̲̳̳k̲̳̳e̲̳̳ picture L̲̳o̲̳̳n̲̳̳g̲̳̳p̲̳o̲̳̳k̲̳̳e̲̳̳ · Jun 4, 2010

A lambda's body has to be a single expression. In Python 2.x, print is a statement. However, in Python 3, print is a function (and a function application is an expression, so it will work in a lambda). You can (and should, for forward compatibility :) use the back-ported print function if you are using the latest Python 2.x:

In [1324]: from __future__ import print_function

In [1325]: f = lambda x: print(x)

In [1326]: f("HI")
HI

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