Python lists – Python list() functions and methods

by Alex
10 лучших редакторов кода Python для Android

How to create a list?

Lists are announced in square brackets [ ]. Список в pythonThe second line of this python list table is the list item index.

z = [3, 7, 4, 2] # Creating a list

In python, lists store an ordered set of elements, which can be of different types. In the example above, the elements are of the same int type. It is not necessary that all elements be of the same type.

# Creation of a list with different data types
heterogenousElements = [3, True, 'Vitya', 2.0]

This list contains int, bool, string, and float.

Accessing the items in the list

Each item has an index assigned to it. It is important to note that in python the index of the first element in the list is 0. Элементы спискаItem with index 0 (highlighted in blue)

z = [3, 7, 4, 2] # creating a list
# call the first element in the list with index 0
print(z[0])
# item with index 0 -> 3

Negative indexing is also supported. Negative indexing starts from the end. Sometimes it’s more convenient to use it to get the last item in the list, because you don’t need to know the length of the list to access the last item. Отрицательная индексация спискаItem with index -1 (highlighted in blue)

# print the last item
>>> print(z[-1])
2

You can also access the same item using positive indices (as shown below). An alternative way to access the last element in the z list.

>>> print(z[3])
2

List slice

Slice is good for getting a subset of values from your list. In the example code below, it will return a list with items from index 0 and not including index 2. Срезы спискаThe first index is written (before : inclusive) and the last (after : ) and not including

# create list
z = [3, 7, 4, 2]
# Outputs items with indexes from 0 to 2 (not including 2)
print(z[0:2])
# output: [3, 7]

Срезы списка 2

# everything but index 3
>>>> print(z[:3])
[3, 7, 4]

Срезы списка 3 The code below returns a list with elements from index 1 to the end.

# from index 1 to the end of the list
>>> print(z[1:])
[7, 4, 2]

Changing items in the list

Изменение списка Lists in Python are modifiable. This means that you can update individual elements of a list after it has been created.

z = [3, 7, 4, 2] # Creating a list
# change the element with index 1 to the string 'fish'
z[1] = 'fish'
print(z)
[3, 'fish', 4, 2]

Methods and Functions of Python Lists

Python lists have different methods that help with programming. This section covers all list methods.

Index Method

The index method returns the position of the first index, with a value of x. In the code below, it returns back 0.

# create a list
>>> z = [4, 1, 5, 4, 10, 4]
>>> print(z.index(4))

Индексы списка You can also specify where you start the search from.

>>> print(z.index(4, 3))
3

list index

The count method

The count method works just as it sounds. It counts the number of times the value appears in the list.

>>> random_list = [4, 1, 5, 4, 10, 4]
>>> print(random_list.count(4))
3

Sort method

метод sortSort the list – the actual code will be: z.sort() The sort method sorts and changes the original list.

z = [3, 7, 4, 2]
z.sort()
print(z)
[2, 3, 4, 7]

Обратная сортировка спискаSorting the list from the highest to the lowest value The code above sorts the list of numbers from smallest to largest. The code below shows how you can sort the list from largest to smallest.

# Sort and reverse the original list from highest to lowest
z.sort(reverse = True)
print(z)
[7, 4, 3, 2]

Note that you can also sort the list of rows from A to Z (or A-Z) and vice versa.

# Sorting the list with strings
names = ["Steve", "Rachel", "Michael", "Adam", "Jessica", "Lester"]
names.sort()
print(names)
['Adam', 'Jessica', 'Lester', 'Michael', 'Rachel', 'Steve']

Append method

list appendAdd value 3 to the end of the list The append method adds an item to the end of the list. This happens in place.

z = [7, 4, 3, 2]
z.append(3)
print(z)
[7, 4, 3, 2, 3]

Remove method

метод removeThe remove method removes the first occurrence of a value in the list.

z = [7, 4, 3, 2, 3]
z.remove(2)
print(z)

The code removes the first occurrence of value 2 from the list z.

[7, 4, 3, 3]

Pop method

метод popz.pop(1) removes the value in index 1 and returns value 4 The pop method removes an item in the specified index. This method will also return the element that was removed from the list. In case you didn’t specify an index, it will by default remove the item at the last index.

z = [7, 4, 3, 3]
print(z.pop(1))
print(z)
4
[7, 3, 3]

The Extend method

Метод Extend The extend method extends a list by adding items. The advantage over append is that you can add lists. Add [4, 5] to the end of z:

z = [7, 3, 3]
z.extend([4,5])
print(z)
[7, 3, 3, 4, 5]

The same could be done using +.

>>> print([1,2] + [3,4])
[7, 3, 3, 4, 5]

Insert method

метод insertInserts [1,2] with index 4 The insert method inserts an element before the specified index.

z = [7, 3, 3, 4, 5]
z.insert(4, [1, 2])
print(z)
[7, 3, 3, 4, [1, 2], 5]

Simple operations on lists

MethodDescribexin sTrue if element x is in the list sxnot in sTrue if element x is not in the list ss1+ s2Combinelist s1 and s2s* n , n * sCopylist s n timeslen(s)List length s, i.e. number of elements insmin(s)Smallest list elementsmax(s)Largest list element ssum(s)Sum of list numbers sfori in list()Go through elements left to right in the for loop Examples of using functions with lists:

>>> list1 = [2, 3, 4, 1, 32]
>>> 2 in list1 # 2 in list1?
True
>>> 33 not in list1 # 33 not in list1?
True
>>> len(list1) # number of list items
5
>>> max(list1) # biggest list item
32
>>> min(list1) # smallest list item
1
>>> sum(list1) # sum of list items
42
# python list generator (list comprehension)
>>> x = [i for i in range(10)]
>>> print(x)
[0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
>>> print(list1.reverse()) # expand list
[32, 1, 4, 3, 2]

The + and *

operators for lists

+

joins two lists.

list1 = [11, 33]
list2 = [1, 9]
list3 = list1 + list2
print(list3)
[11, 33, 1, 9]

* copies the items in the list.

list4 = [1, 2, 3, 4]
list5 = list4 * 3
print(list5)
[1, 2, 3, 4, 1, 2, 3, 4, 1, 2, 3, 4]

Operator in and not in

The in operator checks if an item is in the list. If successful, it returns True, if not, it returns False.

>>> list1 = [11, 22, 44, 16, 77, 98]
>>> 22 in list1
True

Similarly, not in returns the opposite result from the in operator.

>>> 22 not in list1
False

Iterating through a list using the for loop

A list is a sequence. Below is a way that you can use a loop to iterate through all the items in a list.

list1 = [1,2,3,4,5]
for i in list1:
print(i, end=" ")
1 2 3 4 5

Converting a list to a string

How do I convert a list to a string? To convert a list to a string, use the join() method. In Python, it looks like this: ",".join(["a", "b", "c"]) -> "a,b,c". The separator is written in quotes before the join, the list must consist of strings. Here are some useful tips for converting a list into a string (or any other iterable, such as tuple). First, if it is a list of strings, you can simply use join() as follows.

mylist = ['spam', 'ham', 'eggs']
print(', '.join(mylist))
spam, ham, eggs

Using the same method, you can also do the following:

>>> print('\n'.join(mylist))
spam
ham
eggs

However, this simple method does not work if the list contains nonlinear objects, such as integers. If you just want a comma-separated string, you can use this pattern:

list_of_ints = [80, 443, 8080, 8081]
print(str(list_of_ints).strip('[]'))
80, 443, 8080, 8081

Or this one if your objects contain square brackets:

>>>> print(str(list_of_ints)[1:-1])
80, 443, 8080, 8081

Finally, you can use map() to convert each element to a string list and then join them:

>>> print(', '.join(map(str, list_of_ints)))
80, 443, 8080, 8081
>>> print('\n'.join(map(str, list_of_ints)))
80
443
8080
8081

The Python List Test

How do you create a list? All options are correct l = list[1, 2, 3] l = [1, 2, 3] l = list(1, 2, 3) Continue to What this code will output:

a = [ 1, 342, 223, 'Africa', 'Points']
print(a[-3])

‘Africa’ Error 223 342 Continue to What this code will print:

sample = [10, 20, 30]
sample.append(60)
sample.insert(3, 40)
print(sample)

[10, 20, 30, 60, 40] [10, 20, 30, 40] [10, 20, 30, 40, 60] [60, 10, 20, 30, 40] Continue to What this code will output:

lake = ["Python", 51, False, "22"]
lake.reverse()
lake.reverse()
print(lake[-2])

51 -2 [51] False Continue to Which of the following is true? A list cannot contain nested lists We can insert an item at any position in the list All list items must be of the same type Elements of the list can’t duplicate each other Continue to How to get ['bar', 'baz'] from a list

a = ['foo', 'bar', 'baz', 'qux', 'quux']

? print(a[-4:-3]) print(a[1:-2]) print(a[2:3]) print(a[2:4]) print(a[1], a[2]) Continue to How to get 'bar' from a list

x = [10, [3.141, 20, [30, 'baz', 2.718]], 'foo']

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