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ListMethods.md

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List Methods

1.clear()

  • clear() method removes all the elements from a list.

Syntax:

listname.clear()

Example:

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

#Now clear the list using clear() 
lst.clear() 
print(lst) 
#Result:[]

Output:

[1, 2, 3, 4, 5]
[]

2. count()

  • count() method returns the number of elements with the specified value.
  • Any type of (string, number, list, tuple, etc.) Data can be counted using count() method.

Syntax:

lstname.count(value)

Example:

lst=[1, 2,3,4,5,1,4,1,1,1]
cnt=lst.count(1)
print(cnt) 
#Result:5

Output:

5

If string search value put quotes inside count method Example:

color=["red","blue","green","red","yello","orange","red"]
#find out count of red
red_cnt=color.count("red") 
print(red_count) 
#Result:3

Output:

3

count list inside a list

lst=[1, 2,3,4,5,1,4,1,1,1,[8,9]]

cnt=lst.count([8,9])
print(cnt) 
#Result:1

Output:

1

3.index()

  • index() method return the position index of specified value.
  • index() method returns the position at the first occurrence of the specified value

Syntax:

listname.index(value)

Example:

color=["red","blue","green"]
indx=color.index("red")
print(indx) 
#Result:0

Output:

0

4. reverse() 🔚

  • reverse() method reverses the given elements from list.

Syntax:

listname.reverse()

Example 1:

lst=[5,7,8,4]
lst.reverse() 
print(lst)

Output:

[4,8,7,5]

Example 2:

color=["red","blue","green"]
color.reverse() 
print(lst)

Output:

["green","blue","red"]

Once you apply .reverse() on the list you can not get back original list

reversed()

  • The buil-in function reversed() returns a reversed iterator object.

Example:

color=["red","blue","green"]
print("reversed list",list(reversed(color))) 
print("original list ",color) 
#Result:
#reversed list ["green","blue","red"]
#original list   ["red","blue","green"]

Output:

reversed list ['green', 'blue', 'red']
original list  ['red', 'blue', 'green']

5.sort()

  • sort() method sort the list in ascending and descending order
  • sort() method sorts the list ascending by default.

Synatx:

listname.sort(reverse=True|False, key=myFunc)

Example: Sort ascending

lst=[4,3,5,2,1,6]
lst.sort() 
print(lst)

Output:

[1,2,3,4,5,6]

Sort descending

lst=[4,3,5,2,1,6]
lst.sort(reverse=True) 
print(lst)

Output:

[6,5,4,3,2,1]

Note: After sorting done using .sort() method you can not get original list back all position of all element changed we can not recover it.

sorted()

  • Sorting any sequence is very easy in Python using the built-in method sorted() which does all the hard work for you.

  • Sorted() sorts any sequence (list, tuple) and always returns a list with the elements in a sorted manner, without modifying the original sequence.

Syntax:

sorted(iterable object, key, reverse=True/False)

Example:

lst=[4,3,5,2,1,6]
print(sorted(lst)) #sorted list
#Result:[1,2,3,4,5,6]

#print original list
print(lst) 
#Result:[4,3,5,2,1,6]

Output:

[1, 2, 3, 4, 5, 6]
[4, 3, 5, 2, 1, 6]