Starting with a three-dimensional list:
alist = [[[1,2],[3,4]], [[5,6,7],[8,9,10], [12, 13, 14]]]Accessing items in the list:
print(alist[0][0][1])
# 2
# Accesses second element in the first list in the first list
print(alist[1][1][2])
# 10
# Accesses the third element in the second list in the second listPerforming support operations:
alist[0][0].append(11)
print(alist[0][0][2])
# 11
# Appends 11 to the end of the first list in the first listUsing nested for loops to print the list:
for row in alist: #One way to loop through nested lists
for col in row:
print(col)
# [1, 2, 11]
# [3, 4]
# [5, 6, 7]
# [8, 9, 10]
# [12, 13, 14]Note that this operation can be used in a list comprehension or even as a generator to produce efficiencies, e.g.:
[col for row in alist for col in row]
# [[1, 2, 11], [3, 4], [5, 6, 7], [8, 9, 10], [12, 13, 14]]Not all items in the outer lists have to be lists themselves:
alist[1].insert(2, 15)
# Inserts 15 into the third position in the second listAnother way to use nested for loops. The other way is better but I’ve needed to use this on occasion:
for row in range(len(alist)): #A less Pythonic way to loop through lists
for col in range(len(alist[row])):
print(alist[row][col])
# [1, 2, 11]
# [3, 4]
# [5, 6, 7]
# [8, 9, 10]
# 15
# [12, 13, 14]Using slices in nested list:
print(alist[1][1:])
# [[8, 9, 10], 15, [12, 13, 14]]
# Slices still workThe final list:
print(alist)
# [[[1, 2, 11], [3, 4]], [[5, 6, 7], [8, 9, 10], 15, [12, 13, 14]]]