Question

When I printed a list, I got a syntax error when using this method:

print i for i in [1,2,3]

I knew this is ok when using this method:

for i in [1, 2, 3]:
    print i

and I knew that

(i for i in [1, 2, 3])

is a generator object, but I just don’t get it that why

print i for i in [1, 2, 3] 

does’t work. Can anyone give me a clue?

Answer 1

In Python 2, print is a statement, not an expression or a function, so you can’t use it directly in a comprehension. Use this trick:

def f(x): print x
[f(i) for i in [1,2,3]]

Note that (f(i)...) doesn’t work because this just creates a generator which would call f() if you iterated over it. The list comprehension [] actually invokes f().

[EDIT] If you use Python > 2.6, you can achieve the same using

from __future__ import print_function
[print(i) for i in [1, 2, 3]]

Note the () around the argument to print.