Question

How do you apply ‘or’ to all values of a list in Python? I’m thinking something like:

or([True, True, False]) 

or if it was possible:

reduce(or, [True, True, False]) 

Answer 1

The built-in function any does what you want:

>>> any([True, True, False]) True >>> any([False, False, False]) False >>> any([False, False, True]) True 

any has the advantage over reduce of shortcutting the test for later items in the sequence once it finds a true value. This can be very handy if the sequence is a generator with an expensive operation behind it. For example:

>>> def iam(result): ...  # Pretend this is expensive. ...  print 'iam(%r)' % result ...  return result ...  >>> any((iam(x) for x in [False, True, False])) iam(False) iam(True) True >>> reduce(lambda x,y: x or y, (iam(x) for x in [False, True, False])) iam(False) iam(True) iam(False) True 

If your Python’s version doesn’t have any(), all() builtins then they are easily implemented as Guido van Rossum suggested:

def any(S):     for x in S:         if x:             return True     return False  def all(S):     for x in S:         if not x:             return False     return True