CODEWITHSUNDEEP
python
Robert Christie
Robert Christie

Reputation: 20705

How to apply a logical operator to all elements in a python list

I have a list of booleans in python. I want to AND (or OR or NOT) them and get the result. The following code works but is not very pythonic.

def apply_and(alist):
 if len(alist) > 1:
     return alist[0] and apply_and(alist[1:])
 else:
     return alist[0]

Any suggestions on how to make it more pythonic appreciated.

Upvotes: 121

Views: 139136

Answers (6)

fortran
fortran

Reputation: 76157

Logical and across all elements in a_list:

all(a_list)

Logical or across all elements in a_list:

any(a_list)

If you feel creative, you can also do:

import operator
def my_all(a_list):
  return reduce(operator.and_, a_list, True)

def my_any(a_list):
  return reduce(operator.or_, a_list, False)

keep in mind that those aren't evaluated in short circuit, whilst the built-ins are ;-)

another funny way:

def my_all_v2(a_list):
  return len(filter(None,a_list)) == len(a_list)

def my_any_v2(a_list):
  return len(filter(None,a_list)) > 0

and yet another:

def my_all_v3(a_list):
  for i in a_list:
    if not i:
      return False
  return True

def my_any_v3(a_list):
  for i in a_list:
    if i:
      return True
  return False

and we could go on all day, but yes, the pythonic way is to use all and any :-)

By the way, Python has not tail recursion elimination, so don't try to translate LISP code directly ;-)

Upvotes: 229

Xarts
Xarts

Reputation: 77

Here's another solution:

def my_and(a_list):
    return not (False in a_list)

def my_or(a_list):
    return True in a_list

ANDing all elements will return True if all elements are True, hence no False in a list. ORing is similar, but it should return True if at least one True value is present in a list.

Upvotes: 4

Eli Bendersky
Eli Bendersky

Reputation: 273874

The idiom for such operations is to use the reduce function (global in Python 2.X, in module functools in Python 3.X) with an appropriate binary operator either taken from the operator module or coded explicitly. In your case, it's operator.and_

reduce(operator.and_, [True, True, False])

Upvotes: 13

mipadi
mipadi

Reputation: 411390

As the other answers show, there are multiple ways to accomplish this task. Here's another solution that uses functions from the standard library:

from functools import partial

apply_and = all
apply_or = any
apply_not = partial(map, lambda x: not x)

if __name__ == "__main__":
    ls = [True, True, False, True, False, True]
    print "Original: ", ls
    print "and: ", apply_and(ls)
    print "or: ", apply_or(ls)
    print "not: ", apply_not(ls)

Upvotes: 0

Jason Baker
Jason Baker

Reputation: 198877

ANDing and ORing is easy:

>>> some_list = [True] * 100
# OR
>>> any(some_list)
True
#AND
>>> all(some_list)
True
>>> some_list[0] = False
>>> any(some_list)
True
>>> all(some_list)
False

NOTing is also fairly easy:

>>> [not x for x in some_list]
[True, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False, False]

Of course, how you would use those results might require some interesting applications of DeMorgan's theorem.

Upvotes: 34

Frank Krueger
Frank Krueger

Reputation: 71063

Reduce can do this:

reduce(lambda a,b: a and b, alist, True)

As fortran mentioned, all is the most succinct way to do it. But reduce answers the more general question "How to apply a logical operator to all elements in a python list?"

Upvotes: 19

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