Why doesn't print work in a lambda?

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

In cases where I am using this for simple stubbing out I use this:

fn = lambda x: sys.stdout.write(str(x) + "\n")

which works perfectly.

what you've written is equivalent to

def anon():
    return print "x"

which also results in a SyntaxError, python doesn't let you assign a value to print in 2.xx; in python3 you could say

lambda: print('hi')

and it would work because they've changed print to be a function instead of a statement.