Diez B. Roggisch wrote:
Esmail schrieb:
Could someone help confirm/clarify the semantics of the [:] operator
in Python?
a = range(51,55)
############# 1 ##################
b = a[:] # b receives a copy of a, but they are independent
>
# The following two are equivalent
############# 2 ##################
c = []
c = a[:] # c receives a copy of a, but they are independent
No, the both above are equivalent. Both just bind a name (b or c) to a
list. This list is in both cases a shallow copy of a.
############# 3 ##################
d = []
d[:] = a # d receives a copy of a, but they are independent
This is a totally different beast. It modifies d in place, no rebinding
a name. So whover had a refernce to d before, now has a changed object,
whereas in the two cases above, the original lists aren't touched.
To demonstrate what Diez is saying:
a = range(51,55)
d = []
x = d
d[:] = a
print x #hey, I didn't change x...oh, yeah
-tkc
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