Emanuele D'Arrigo wrote:
On 6 Mar, 19:46, Gary Herron <gher...@islandtraining.com> wrote:
It is an implementation choice (usually driven by efficiency considerations) to
choose when two strings with the same value are stored in memory once or twice.
In order for Python to recognize when a newly created string has the same
value as an already existing string, and so use the already existing value, it
would need to search *every* existing string whenever a new string is created.
Clearly that's not going to be efficient. However, the C implementation of
Python does a limited version of such a thing -- at least with strings of
length 1.
Gary, thanks for your reply: your explanation does pretty much answer
my question. One thing I can add however is that it really seems that
non-alphanumeric characters such as the forward slash make the
difference, not just the number of characters. I.e.
a = "aaaaaaaaaaaaaaaaaaaaaaaaaaa"
b = "aaaaaaaaaaaaaaaaaaaaaaaaaaa"
a is b
True
a = "/aaaaaaaaaaaaaaaaaaaaaaaaaaa"
b = "/aaaaaaaaaaaaaaaaaaaaaaaaaaa"
a is b
False
I just find it peculiar more than a nuisance, but I'll go to the
blackboard and write 100 times "never compare the identities of two
immutables". Thank you all!
Unless you are *trying* to discern something about the implementation
and its attempt at efficiencies. Here's several more interesting example:
>>> 101 is 100+1
True
>>> 1001 is 1000+1
False
>>> 10*'a' is 5*'aa'
True
>>> 100*'a' is 50*'aa'
False
Gary Herron
Manu
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