On 1/10/2011 8:07 AM Karim said...
Hello All,
I am not a beginner in Python language but I discovered a hidden
property of immutable elements as Numbers and Strings.
s ='xyz'
>>> t = str('xyz')
>>> id(s) == id(t)
True
Thus if I create 2 different instances of string if the string is
identical (numerically).
well, not predictably unless you understand the specifics of the
implementation you're running under.
>>> from string import letters
>>> longstring = letters*100
>>> otherstring = letters*100
>>> id(longstring)
12491608
>>> id (otherstring)
12100288
>>> shortstring = letters[:]
>>> id(letters)
11573952
>>> id(shortstring)
11573952
>>>
I get the same object in py db. It could be evident but if I do the same
(same elements) with a list it
will not give the same result. Is-it because of immutable property of
strings and numbers?
It has to do with Interning -- see eg
http://docs.python.org/library/functions.html#intern
Generally, the shorter strings are interned to speed up dictionary
access. At this point, I'd characterize the coincidence of id()s as
more of an implementation detail side effect than anything else.
Emile
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