How to use: while not in

Question

I'm trying to check if a list has no member as boolean operator AND, OR, NOT.

I use:

while ('AND' and 'OR' and 'NOT') not in list:
  print 'No boolean operator'

However, when my input is: a1 c2 OR c3 AND, it prints 'No boolean operator', which means this list is considered no boolean operator in it by using above loop sentence.

Hope somebody can help to correct.

Thanks, Cindy

Answer 1

The expression 'AND' and 'OR' and 'NOT' always evaluates to 'NOT', so you are effectively doing

while 'NOT' not in some_list:
    print 'No boolean operator'

You can either check separately for all of them

while ('AND' not in some_list and 
       'OR' not in some_list and 
       'NOT' not in some_list):
    # whatever

or use sets

s = set(["AND", "OR", "NOT"])
while not s.intersection(some_list):
    # whatever

Answer 2

Using sets will be screaming fast if you have any volume of data

If you are willing to use sets, you have the isdisjoint() method which will check to see if the intersection between your operator list and your other list is empty.

MyOper = set(['AND', 'OR', 'NOT'])
MyList = set(['c1', 'c2', 'NOT', 'c3'])

while not MyList.isdisjoint(MyOper):
    print "No boolean Operator"

http://docs.python.org/library/stdtypes.html#set.isdisjoint

Answer 3

anding strings does not do what you think it does - use any to check if any of the strings are in the list:

while not any(word in list_of_words for word in ['AND', 'OR', 'NOT']):
    print 'No boolean'

Also, if you want a simple check, an if might be better suited than a while...