Python: Sending the print function as a parameter

Question

My professor had mentioned that it's possible to pass functions like print as a parameter, but when I try and actually implement it I get a syntax error. Is it something small that I am missing here?

 def goTime(sequence, action):
    for element in sequence:
       action(element)

 def main():
    print("Testing Begins")
    test = list ( range( 0 , 20, 2) ) 
    goTime(test, print)
    print("Testing Complete")

Upon running the following, I receive this syntax error:

goTime(test, print)
                 ^
SyntaxError: invalid syntax

If I define my own function that uses print, it works, like so:

def printy(element):
   print(element)

def goTime(sequence, action):
   for element in sequence:
      action(element)

def main():
   print("Testing Begins")
   test = list ( range( 0 , 20, 2) ) 
   goTime(test, printy)
   print("Testing Complete")

@roippi you can also do `from __future__ import print_function` to get it in earlier versions. — Mark Ransom, Jan 31 '14 at 17:59
Bah, I was using an older version. Stupid mistake, thanks guys. — Talen Kylon, Jan 31 '14 at 18:00
Just a note: Python2.7 ain't just _an older version of python_. Is still heavily used :) — Paulo Bu, Jan 31 '14 at 20:29

Paulo Bu · Answer 1 · 2014-01-31T18:05:51.057

5

In Python 3 that will work out of the box. In Python 2.7 however, you can do:

from __future__ import print_function
def foo(f,a):
    f(a)

foo(print,2)
2

Note that in Python2.7 after you do from __future__ import print_function you won't be able to use print like a keyword any more:

>>> from __future__ import print_function
>>> print 'hi'
  File "<stdin>", line 1
    print 'hi'
             ^
SyntaxError: invalid syntax

Although I think your professor only wanted to make a point that functions in Python are first class citizens (ie: objects) and they can be passed around as any other variable. He used a controversial example though :)

Hope this helps!

edited Jan 31 '14 at 18:05

answered Jan 31 '14 at 18:00

Paulo Bu

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I don't think you need the ticks around `print_function`. – Mark Ransom Jan 31 '14 at 18:00
@MarkRansom Lol, definitely not needed. Sorry about that :) – Paulo Bu Jan 31 '14 at 18:02

score 1 · Answer 2 · edited May 23 '17 at 10:33

1

You can't pass print in Python2, because it's a keyword rather than a function. It's possible in Python3.

You can try to import new print function from future. Check this question:

How to gracefully deal with failed future feature (__future__) imports due to old interpreter version?

and then you can use it as a function.

edited May 23 '17 at 10:33

Community

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answered Jan 31 '14 at 17:59

gruszczy

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score 0 · Answer 3 · answered Jan 31 '14 at 18:25

0

You can try sys.stdout

import sys

def printy(element):
    sys.stdout.write(str(element)+'\n')

answered Jan 31 '14 at 18:25

afkfurion

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score 0 · Answer 4 · answered Jan 09 '21 at 23:19

0

In python2 You can wrap print inside of a wrapper function and pass that:

def PrintWrapper(arg):
    print(arg)

def MyFunc(x, func):
    func(x)

# call the function with the wrapper as an argument
MyFunc("Hello world", PrintWrapper)

answered Jan 09 '21 at 23:19

Reinaldo Aguiar

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Python: Sending the print function as a parameter

4 Answers4