Summary of python list method

List.append() method

purpose
The append() method is used to add a new object at the end of the list.
grammar

list.append(obj)

parameter

• obj: the object added to the end of the list.

Return value
There is no return value for this method, but the original list will be modified.

Example

list1 = ['hello', 'world', 'python']
list1.append('pycharm')
print ("After updating list1 : ", list1)

Output result

After update, LIST1: ['Hello ',' world ',' Python ',' pycharm ']

List.count() method

purpose
The count() method is used to count the number of times an element appears in the list.
grammar

list.count(obj)

parameter

• obj: objects counted in the list.

Return value
Returns the number of times an element appears in the list.
Example

List1 = ['hello', 'python', 323, 'hello', 'python', 323];

print ("323 Element number : ", List1.count(323))
print ("python Element number : ", List1.count('python'))

Output results:

323 number of elements: 2
 Number of python elements: 2

List.extend() method

purpose
The extend() function is used to append multiple values in another sequence at the end of the list at one time (extending the original list with a new list).
grammar

list.extend(seq)

parameter

• -seq: list of elements, which can be list, tuple, set or dictionary. If it is a dictionary, only the key will be added to the end of the original list as an element in turn.

Return value
The method does not return a value, but adds new list content to the existing list.
Example

list1 = ['hello', 'world', 'python']
list2=list(range(3)) # Create a list of 0-2
list1.extend(list2)  # Extended list
print ("Expanded list:", list1)

Output result

Expanded list: ['Hello ',' world ',' Python ', 0, 1, 2,]

Do not use data type instance

# Language list
language = ['French', 'English', 'German']
 
# tuple
language_tuple = ('Spanish', 'Portuguese')
 
# aggregate
language_set = {'Chinese', 'Japanese'}
 
# Add tuple element to end of list
language.extend(language_tuple)
 
print('New list: ', language)
 
# Add collection elements to the end of the list
language.extend(language_set)
 
print('New list: ', language)

Output result

New list: ['french ',' English ',' German ',' Spanish ',' Portugal ']
New list: ['french ',' English ',' German ',' Spanish ',' Portuguese ',' Japanese ',' Chinese ']

List.index() method

purpose
The index() function is used to find the index position of the first match of a value from the list.
grammar

list.index(x[, start[, end]])

parameter

• x -- the object to find.
• start -- optional, the starting position of the search.
• End -- optional, the end position of the search.

Return value
This method returns the index location of the lookup object, and throws an exception if the object is not found.

Example

list1 = ['Google', 'Runoob', 'Taobao']
print ('Runoob Index value is', list1.index('Runoob'))
print ('Taobao Index value is', list1.index('Taobao'))

Output result

Runoob index value is 1
 Taobao index value is 2

Example 2

list1 = ['Google', 'Runoob', 'Taobao', 'Facebook', 'QQ']
# Search from specified location
print ('Runoob Index value is', list1.index('Runoob',1))

Output result

Runoob index value is 1

List.insert() method

purpose
The insert() function inserts the specified object into the specified location in the list.
grammar

list.insert(index, obj)

parameter

• Index – the index location where the object obj needs to be inserted.
• obj – the object to insert into the list.

Return value
The method does not return a value, but inserts the object at the location specified in the list.
Example

list1 = ['Google', 'Runoob', 'Taobao']
 list1.insert(1, 'Baidu')
print ('List after element insertion : ', list1)

Output result

After inserting elements in the list: ['google ',' Baidu ',' runoob ',' Taobao ']

List.pop() method

purpose
The pop() function removes an element from the list (the last element by default) and returns the value of that element.
grammar

list.pop([index=-1])

parameter

• Index – optional parameter. To remove the index value of a list element, it cannot exceed the total length of the list. The default value is index=-1. Delete the last list value.
  Return value
  This method returns the element object removed from the list.
  Example

list1 = ['Google', 'Runoob', 'Taobao']
list1.pop()
print ("The list is now : ", list1)
list1.pop(1)
print ("The list is now : ", list1)

Output result

The list is now: ['google ',' runoob ']
The list is now: ['Google ']

Give an example

list1 = ['Google', 'Runoob', 'Taobao']
list_pop=list1.pop(1)
print ("Deleted items are :", list_pop)
print ("The list is now : ", list1)

Output result

The deleted element is: Runoob
 The list is now: ['google ',' Taobao ']

List.remove() method

purpose
The remove() function removes the first match for a value in the list.
grammar

list.remove(obj)

parameter

• obj: the object to be removed from the list.

Return value
The method does not return a value but removes the first match for a value in the list.
Example

list1 = ['Google', 'Runoob', 'Taobao', 'Baidu']
 list1.remove('Taobao')
print ("The list is now : ", list1)
 list1.remove('Baidu')
print ("The list is now : ", list1)

Output result

The list is now: ['google ',' runoob ',' Baidu ']
The list is now: ['google ',' runoob ']

List.reverse() method

purpose
The reverse() function is used to reverse the elements in the list.
grammar

list.reverse()

parameter
nothing
Return value
The method does not return a value, but sorts the elements of the list in reverse.
Example

list1 = ['Google', 'Runoob', 'Taobao', 'Baidu']
list1.reverse()
print ("After list reversal: ", list1)

Output result

After the list is reversed: ['baidu ',' Taobao ',' runoob ',' Google ']

List.sort() method

purpose
The sort() function is used to sort the original list. If you specify parameters, the comparison function specified by the comparison function is used.
grammar

list.sort( key=None, reverse=False)

parameter

• key - the element mainly used for comparison. There is only one parameter. The specific function parameter is taken from the iteratable object. Specify an element in the iteratable object to sort.
• Reverse - collation, reverse = True descending, reverse = False ascending (default).

Return value
This method does not return a value, but sorts the objects in the list.
Example

aList = ['Google', 'Runoob', 'Taobao', 'Facebook']
 
aList.sort()
print ( "List : ", aList)

Output result

List :  ['Facebook', 'Google', 'Runoob', 'Taobao']

Descending instance

# list
vowels = ['e', 'a', 'u', 'o', 'i']
 
# Descending order
vowels.sort(reverse=True)
 
# Output result
print ( 'Descending output:', vowels )

Output result

Output in descending order: ['u ',' o ',' I ',' e ',' a ']

Specify the output instance of element sorting in the list

# Get the second element of the list
def takeSecond(elem):
    return elem[1]
 
# list
random = [(2, 2), (3, 4), (4, 1), (1, 3)]
 
# Specify the second element sort
random.sort(key=takeSecond)
 
# Output class
print ('Sort list:', random)

Output result

Sort list: [(4, 1), (2, 2), (1, 3), (3, 4]]

List.clear() method

purpose
The clear() function is used to clear the list, similar to del a [:].
grammar

list.clear()

parameter
nothing
Return value
The method has no return value.
Example

list1 = ['Google', 'Runoob', 'Taobao', 'Baidu']
list1.clear()
print ("After the list is cleared : ", list1)

Output result

After the list is cleared: []

List.copy() method

purpose
The copy() function copies the list, similar to a [:].
grammar

list.copy()

parameter
nothing
Return value
Returns the new list after replication.
Example

list1 = ['Google', 'Runoob', 'Taobao', 'Baidu']
 list2 = list1.copy()
print ("list2 list: ", list2)

Output result

list2 list:  ['Google', 'Runoob', 'Taobao', 'Baidu']