python - NameError: global name 'reduce' is not defined

29
votes

I'm new to Python. Would you please tell me what's wrong with the following code? When I run it, I got an error message of "NameError: global name 'reduce' is not defined". I asked Goolge but it's useless. :(

def main():
    def add(x,y): return x+y
    reduce(add, range(1, 11))

if __name__=='__main__':
    main()
2
pythonreduce
One of the reasons reduce was moved out of the built-ins was because it was frequently being used for addition, where sum is preferable (in this case, you could just do sum(range(1, 11)), or sum(xrange(1, 11)) in Python 2). Note also that there is an add function equivalent to yours in the standard library: operator.add. – James

2 Answers

60
votes

I'm going to guess that:

  1. You are using Python 3, and
  2. You are following a tutorial designed for Python 2.

The reduce function, since it is not commonly used, was removed from the built-in functions in Python 3. It is still available in the functools module, so you can do:

import functools

def main():
    def add(x,y): return x+y
    functools.reduce(add, range(1, 11))
10
votes

Also

# Import reduce from functools
from functools import reduce

Allows you to use reduce as though it were a built in function.

def main():
    def add(x,y): return x+y
    reduce(add, range(1, 11))