Python Basic Doubt

[Gary Herron]

On 08/10/2013 11:00 AM, Xavi wrote:
> Hello,
>
> El 10/08/2013 18:40, Tim Chase escribió:
>> Generally, if you are using the "is" operator to compare against
>> anything other than None, you're doing it wrong. There are exceptions
>> to this, but it takes knowing the particulars.
>
> Now I have one doubt, I use 'is' to compare basic types in python 3, 
> for example .-
>
> v = []
> if type(v) is list:
>     print('Is list...')
>
> Because I think it is more clear and faster than .-
> type(v) == [].__class__  ... or ... isinstance(v, list)
>
> Is this correct?
> Thanks.

No!  Don't do that!  If you want to compare values use the "==" operator.

This is an oversimplification, but generally useful for all beginner 
(and most advanced) programmers:
     Don't use "is" for comparisons.  Use "==".
It 20 years of programming Python, I've *needed* to use "is" ... only 
once or twice.

Beyond that, there is a small batch of comparisons where "is" is 
slightly more Pythonic, but not really necessary.  And beyond that, 
there are several instances where the difference between "is" and "=="" 
are important.

Mostly, using "is" is inappropriate and will get you into compassions 
that depend on implementation details.  For instance don't use "is" 
until you understand this:

q:~> python3
Python 3.3.1 (default, Apr 17 2013, 22:32:14)
[GCC 4.7.3] on linux
Type "help", "copyright", "credits" or "license" for more information.

 >>> 101 is 1+100
True

 >>> 1001 is 1+1000
False

Gary Herron