On Sat, 25 Apr 2015 12:50 am, subhabrata.bane...@gmail.com wrote:
> Dear Group,
>
> I am trying to understand the use of Boolean operator in Python. I am
> trying to write small piece of script, as follows,
>
> def input_test():
> str1=raw_input("PRINT QUERY:")
> if "AND" or "OR" or "NOT" in str1:
> print "It is a Boolean Query"
> elif "AND" or "OR" or "NOT" not in str1:
> print "It is not a Boolean Query"
> else:
> print "None"
First problem: why do you sometimes return "None"? You have two possible
answers: either something is a boolean query, or it is not. There is no
third choice. ("It's a boolean query, but only on Wednesdays.")
So your code you have if...else and no "elif" needed.
if <test for boolean query>:
print "It is a Boolean Query"
else:
print "It is not a Boolean Query"
Now let us look at your test for a boolean query:
"AND" or "OR" or "NOT" in str1
How does a human reader understand that as English?
if "AND" is in the string, or "OR" is in the string, or "NOT"
is in the string, then it is a boolean query.
But sadly, that is not how Python sees it. Python sees it as:
if "AND" is a true value, or if "OR" is a true value,
or if "NOT" is in the string, then it is a boolean query.
"AND" is always a true value. All strings except for the empty string "" are
true values, so expressions like:
if X or Y or Z in some_string
will always be true, if X or Y are true values.
You need to re-write your test to be one of these:
# version 1
if "AND" in str1 or "OR" in str1 or "NOT" in str1:
print "It is a Boolean Query"
else:
print "It is not a Boolean Query"
# version 2
if any(word in str1 for word in ("AND", "OR", "NOT")):
print "It is a Boolean Query"
else:
print "It is not a Boolean Query"
--
Steven
--
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