possible python bug here

[manuel]

In the sample below, the foo function modify the b list,
but I think it should modify only c, not b! It work
correctly if if b is one dimension list instead two.

def foo(aList):
print "use foo..."
aList[2][0] += .35
aList[2][1] += .35
aList[2][2] += .35

p = [2.5,2.5,2.5]
b = [p,p,p,p]

c=b[:] #c is a totally new list cloned from b, it's not an alias!

print "b = ",b[2]

foo(c) #The argument is c, not b! Why b is modified too?

print "b = ", b[2]# after foo(c), the list b now is different!

 

[Peter Kleiweg]

manuel schreef:

In the sample below, the foo function modify the b list,
but I think it should modify only c, not b! It work
correctly if if b is one dimension list instead two.

def foo(aList):
print "use foo..."
aList[2][0] += .35
aList[2][1] += .35
aList[2][2] += .35

p = [2.5,2.5,2.5]
b = [p,p,p,p]

c=b[:] #c is a totally new list cloned from b, it's not an alias!

No it isn't. You didn't make a deep copy.

 

[manuel]

manuel schreef:

c=b[:] #c is a totally new list cloned from b, it's not an alias!

No it isn't. You didn't make a deep copy.

Oh..thank you very much!

 

[Tuure Laurinolli]

In the sample below, the foo function modify the b list,
but I think it should modify only c, not b! It work
correctly if if b is one dimension list instead two.

def foo(aList):
print "use foo..."
aList[2][0] += .35
aList[2][1] += .35
aList[2][2] += .35

p = [2.5,2.5,2.5]

Here you bind the name p to a list.

b = [p,p,p,p]

Here you bind the name b to a list, which has four references to list p

c=b[:] #c is a totally new list cloned from b, it's not an alias!

Here you bind the name c to a list, which has four copies of the
references to list p

print "b = ",b[2]

Here you print the third reference to p of list b

foo(c) #The argument is c, not b! Why b is modified too?

Here you modify the third reference to p of list c

print "b = ", b[2]# after foo(c), the list b now is different!

Here you print the third reference to p of list b, it's still just
reference to list (originally bound to) p.

Note that also the other references to the changed list (b[0:4], c[0:4],
p) refer to the same changed list.