Python Language Tutorial => Accessing values in nested list

Example

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 list

Performing 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 list

Using 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 list

Another 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 work

The final list:

print(alist)
#[[[1, 2, 11], [3, 4]], [[5, 6, 7], [8, 9, 10], 15, [12, 13, 14]]]

PDF - Download Python Language for free

Previous Next

Python Language

Fastest Entity Framework Extensions

Example

Got any Python Language Question?

Python Language

Python Language List Accessing values in nested list

Fastest Entity Framework Extensions

Example

Got any Python Language Question?