Re: Is vs Equality Operator

[Gary Herron]

Good Z wrote:

Hello,
I am having problem in using is. Here is what i am doing.

Short answer: Use == for equality. Don't use "is". Ever!
(Especially if you are a newbie.)

Longer answer: In a dozen years of programming Python, the only time I
use "is" is when testing for something like
if x is None
but, even then
if x == None
works just as well, and in any case, there is usually a better way.
(See below.)

Don't use "is" until you can explain the following

>>11 is 10+1

True

>>100001 is 100000+1

False

>
x=''
if x is None or x is '':
return 1

Both None and an empty string (and empty lists, empty dictionaries,
empty sets, and numeric values of 0 and 0.0) all evaluate a False in an
if statement, so the above if statement can be written as

if not x:
return 1

If you have to test for None, just do
if not x:

If you have to differentiate between a value of None and something that
evaluates to False (e.g., and empty list) then do
if x is None:
# handle None explicitly
elif not x:
# handle empty list

>
The above statement does not return value 1.

If i changed the above check to
if x == None or x == '':
return 1
Now it works fine.

Any idea. What is happening here. I am using python 2.4.4 on ubuntu.

Mike

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