On 2017-08-14 20:21, Mok-Kong Shen wrote:
[snip]
I could more or less understand that in test() alist is interpreted as
local but in the extended program below in test2() I first write the
same as in test1(), after which I logically assume that the name alist
is now known as global and then I write alist=[30,60,90] but that
doesn't have any effect globally, since I get the output:
[1, 2, 3]
[3, 6, 9]
[3, 6, 9]
Could you please explain that?
M. K. Shen
---------------------------------------------------------
def test(alist):
alist=[3,6,9]
return
def test1(alist):
alist[0],alist[1],alist[2]=3,6,9
return
def test2(alist):
At entry, "alist" is a local name that refers to the list that was
passed in:
alist ---> [1,2,3]
Now you change values in that list:
alist[0],alist[1],alist[2]=3,6,9
alist ---> [3,6,9]
You've modified the list that was passed in.
You then bind the local name "alist" to a new list.
alist=[30,60,90]
alist ---> [30,60,90] # This is a new list.
At exit, "alist" refers to a different list from the one that was passed in.
return
ss=[1,2,3]
test(ss)
print(ss)
test1(ss)
print(ss)
test2(ss)
print(ss)
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