On 30/03/07, Christopher Spears <[EMAIL PROTECTED]> wrote:
> What I can't remember is what is 'or' in python. For
> example, what if I want the loop to skip apples and
> pears? I tried this:
>
> >>> for f in fruit:
> ... if f != "apples" or "pears":
> ... print f
> ... print "This is not an apple or pear"
> ...
> apples
> This is not an apple or pear
> pears
> This is not an apple or pear
> oranges
> This is not an apple or pear
> >>>
>
> Actually maybe my problem is not asking the right
> question? Should I be looking for 'and' instead of
> 'or' ?
Hi Christopher,
"or" is used to combine two boolean expressions. What you wrote is
equivalent to:
for f in fruit:
if (f != "apples") or ("pears"):
# etc
So python first checks the truth of (f != "apples"). If this is true,
it continues to the body of the if statement. If this is false,
python checks the truth of ("pears"). Because "pears" is a nonempty
string, it is always true, and so python continues to the body of the
if statement anyway.
You have a few options to correct your code. Consider the following:
for f in fruit:
if f == "apples" or f == "pairs":
print f, "is an apple or a pair."
This will check if f is either "apples" or "pairs". You can then invert that:
for f in fruit:
if not (f == "apples" or f == "pairs"):
print f, "is not an apple or pair."
You could then use DeMorgan's law to convert this to:
for f in fruit:
if f != "apples" and f != "pairs":
print f, "is not an apple or pair."
Finally, you have one more option, using the "in" operator:
for f in fruit:
if f not in ["apples", "pairs"]:
print f, "is not an apple or pair."
HTH!
--
John.
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