Emanuele D'Arrigo wrote:
Hi everybody,
while testing a module today I stumbled on something that I can work
around but I don't quite understand.
*Do NOT use "is" to compare immutable types.* **Ever! **
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 Herron
a = "a"
b = "a"
a == b
True
a is b
True
c = "/a"
d = "/a"
c == d
True # all good so far
c is d
False # eeeeek!
Why c and d point to two different objects with an identical string
content rather than the same object?
Manu
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