ΘΕΜΑ: αντιγραφή list

A = [ ]
B = [ ]
 
for i in range(2):
 
  A.append( [ ] )
  B.append( [ ] )
 
A = [ [ 1 , 2 ] , [ 3 , 6 ] ]
 
B = list( A )
 
A[ 0 ][ 0 ] = B[ 0 ][ 0 ] * 2
 
print( A )
print( B )

a = [1, 2, 3, 4]  # Create a list
b = []            # Create another list
 
c = a             # No list is created here. c justs "points" to a
 
c[0] = 0          # Changing the first item of both a and c lists
 
d = list(a)       # Creating a new list. d is a copy of a
e = a[:]          # Creating another list. e is a copy of a too.

a = [2,2,2]   # create a list
b = a         # b "points" to a
c = list(a)   # c is a copy of a
 
id(a)
id(b)
id(c)

>>> a = [[1,2],[3,4]]
>>> b = [[7,8],[9,0]]
>>> id(a[0][0]) == id(b[0][0])   # Check if a[0][0] "points" to b[0][0]
False                            # It doesn't
 
>>> a[0][0] = b[0][0]            
>>> id(a[0][0]) == id(b[0][0])   # Check if a[0][0] "points" to b[0][0]
True                             # It does
 
>>> a
[[7, 2], [3, 4]]
>>> b
[[7, 8], [9, 0]]
 
>>> a[0][0] = b[0][0] * 2
>>> id(a[0][0]) == id(b[0][0])
False
 
>>> a
[[14, 2], [3, 4]]
>>> b
[[7, 8], [9, 0]]

>>> a = [[1,2],[3,4]]
>>> b = list(a)
>>> id(a) == id(b)
False                     # As expected! But...
>>> id(a[0][0]) == id(b[0][0])
True                      # Each element of b "points" at the same object as a!!!

a = [1, 2, 3]
b = []
b.append([i for i in a])
 
id(a[0]) == id(b[0])         # Should evaluate to False

# "Wrong" behavior
inner = [0] * 10
outer = [inner] * 5
outer[0][2] = 1
print outer
 
# "Right behavior
outer = [[0] * 10 for i in range(5)]
outer[0][2] = 1
print outer