Python LIST HowTo (Page: 1)

List in Python is a traditional array with a lot of methods of managing it. Every cell of list can have it’s own type.

How to remove first element from list in Python

There are few different ways to remove first element from list in Python.

1. removing element with list.pop() function

Function pop(i) will remove element number i and return it. If this element is not present – function will rise an error: IndexError

list = [1,2,3,4,5]
first = list.pop(0)
print(first)    # 1
print(list)     # [2,3,4,5]

2. removing element with del function

Function del(list[i]) will remove given element. If this element is not present – function will rise an error: IndexError

list = [1,2,3,4,5]
del(list[0])
print(list)     # [2,3,4,5]

3. removing element with list.remove() function

Function list.remove(list[i]) will remove given element. If this element is not present – function will rise an error: IndexError

list = [1,2,3,4,5]
list.remove(list[0])
print(list)     # [2,3,4,5]

4. removing element with slicing

slices will produce new list with subset of elements. Making this list from second element and assigning this new list to our list will do remove first element

list = [1,2,3,4,5]
list = list[1:]
print(list)     # [2,3,4,5]

How to remove few element from list in Python

1. removing few element with del function

Function del(list[i:j]) will remove elements described in this slice. If some of those elements are not present – function will not do any action against absent elements

list = [1,2,3,4,5]
del(list[1:3])
print(list)  # [1, 4, 5]

2. removing few element with slicing

Removing few elements with slicing is actually reverse task. We can leave untouched few elements with slicing.

list = [1,2,3,4,5]
list = list[1:4]
print(list)     # [2,3,4] – only selected elements left in the list

So if you want to remove selected slice [1:4], you need to use concatenation of two parts

list = [1,2,3,4,5]
list = list[0:1]+list[4:]
print(list)     # [2,3,4]

How to compare two lists

If you need to compare two lists in Python you have two different cases. What do you want to know – is the elements are the same in the list, or they are stored in the same order as well.

How to compare two lists for full identity

Use operator == to make full comparison of two lists

L1 = [1, 2, 3, 4]
L2 = [1, 3, 2, 4]
print(L1 == L2) # False

How to compare two lists for content only

If you are interesting to compare that two lists contains the same elements without comparing order, the easiest way is to compare sorted lists. Use operator == over the sorted() function

L1 = [1, 2, 3, 4]
L2 = [1, 3, 2, 4]
print(sorted(L1) == sorted(L2)) # True

How to iterate over list in Python

Iteration with range(len())

Traditional way for iterate through the list with indexes is to use range(len()) set of functions.

data = [1,-3,5,-4,8]
for idx in range(len(data)): # idx - index
    print(idx, data[idx])    # data[idx] - list element for changing

Iteration over values in the list

For most of the common tasks it is easier to iterate over the values of the list. Yuo should understand, that val is a shallow copy of the value. Modification of val will not make any impact on the original list

data = [1,-3,5,-4,8]
for val in data:          # val - value of each element
    print(val, end=', ')  # 1, -3, 5, -4, 8
    val = 10 
print( data )             # 1, -3, 5, -4, 8

Iteration with enumerate()

enumerate() is a very convenient build-in function, also preferable to iterate over the list in Python.

data = [1,-3,5,-4,8]
for idx, val in enumerate(data): # idx - index
    data[idx] = 5;               # val - list element for using
    print(idx, data[idx], val)   # data[idx] - list element for changing

Go to Page: 1; 2; 3;

Published: 2021-09-13 08:23:41
Updated: 2021-10-24 11:58:41