On Friday, April 24, 2015 at 8:45:04 PM UTC+5:30, Steven D'Aprano wrote:
> On Sat, 25 Apr 2015 12:50 am,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
Thanks Steven for taking so much of your valuable time to make me understand
and nice guidance. Ian your suggestion worked well. Thank you. Regards,
Subhabrata Banerjee.
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