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Python List Methods
Master the essential methods for manipulating and working with Python lists efficiently.
append()
Adds an element at the end of the list
Example
Add an element to the animals list:
animals = ['cat', 'dog', 'rabbit']
animals.append('fish')
print(animals)
# Output: ['cat', 'dog', 'rabbit', 'fish']Definition and Usage
The append() method appends an element to the end of the list.
Syntax
list.append(elmnt)
Parameter Values
| Parameter | Description |
|---|---|
elmnt |
Required An element of any type (string, number, object etc.) |
clear()
Removes all elements from the list
Example
Remove all elements from the animals list:
animals = ['cat', 'dog', 'rabbit']
animals.clear()
print(animals)
# Output: []Definition and Usage
The clear() method removes all elements from the list.
Syntax
list.clear()
Parameter Values
| Parameter | Description |
|---|---|
| No parameters | |
copy()
Returns a copy of the list
Example
Create a copy of the animals list:
animals = ['cat', 'dog', 'rabbit']
new_animals = animals.copy()
print(new_animals)
# Output: ['cat', 'dog', 'rabbit']Definition and Usage
The copy() method returns a copy of the list.
Syntax
list.copy()
Parameter Values
| Parameter | Description |
|---|---|
| No parameters | |
count()
Returns the number of elements with the specified value
Example
Count how many times 'cat' appears in the animals list:
animals = ['cat', 'dog', 'rabbit', 'cat', 'fish']
x = animals.count('cat')
print(x)
# Output: 2Definition and Usage
The count() method returns the number of elements with the specified value.
Syntax
list.count(value)
Parameter Values
| Parameter | Description |
|---|---|
value |
Required Any type (string, number, list, etc.). The value to search for |
extend()
Adds all elements from an iterable to the end of the list
Example
Add elements from tropical list to the fruits list:
fruits = ['apple', 'banana', 'cherry']
tropical = ['mango', 'pineapple', 'papaya']
fruits.extend(tropical)
print(fruits)
# Output: ['apple', 'banana', 'cherry', 'mango', 'pineapple', 'papaya']Definition and Usage
The extend() method adds all elements from an iterable (list, tuple, string, etc.) to the end of the current list. This modifies the original list in place.
Syntax
list.extend(iterable)
Parameter Values
| Parameter | Description |
|---|---|
iterable |
Required Any iterable (list, tuple, set, dictionary, string, etc.). The elements to add to the list |
index()
Returns the index of the first element with the specified value
Example
Find the position of the value 'cherry' in the fruits list:
fruits = ['apple', 'banana', 'cherry', 'orange']
x = fruits.index('cherry')
print(x)
# Output: 2Definition and Usage
The index() method returns the position of the first occurrence of the specified value. If the value is not found, it raises a ValueError exception.
Syntax
list.index(elmnt, start, end)
Parameter Values
| Parameter | Description |
|---|---|
elmnt |
Required Any type. The value to search for |
start |
Optional. An integer specifying at which position to start the search. Default is 0 |
end |
Optional. An integer specifying at which position to end the search. Default is the end of the list |
insert()
Adds an element at the specified position
Example
Insert the value 'orange' at position 1 in the fruits list:
fruits = ['apple', 'banana', 'cherry']
fruits.insert(1, 'orange')
print(fruits)
# Output: ['apple', 'orange', 'banana', 'cherry']Definition and Usage
The insert() method inserts an element at the specified position in the list. Existing elements are shifted to the right to make room for the new element.
Syntax
list.insert(position, element)
Parameter Values
| Parameter | Description |
|---|---|
position |
Required A number specifying the position where the element should be inserted |
element |
Required Any type (string, number, object, etc.). The element to insert |
pop()
Removes and returns the element at the specified position
Example
Remove and return the element at position 1 from the animals list:
animals = ['cat', 'dog', 'rabbit', 'hamster']
x = animals.pop(1)
print(x)
# Output: dog
print(animals)
# Output: ['cat', 'rabbit', 'hamster']Definition and Usage
The pop() method removes the element at the specified position and returns it. If no position is specified, it removes and returns the last element in the list.
Syntax
list.pop(position)
Parameter Values
| Parameter | Description |
|---|---|
position |
Optional. A number specifying the position of the element to remove. Default is -1 (the last element) |
remove()
Removes the first occurrence of the specified value
Example
Remove 'rabbit' from the animals list:
animals = ['cat', 'dog', 'rabbit', 'hamster']
animals.remove('rabbit')
print(animals)
# Output: ['cat', 'dog', 'hamster']Definition and Usage
The remove() method removes the first occurrence of the element with the specified value. If the value is not found, it raises a ValueError exception.
Syntax
list.remove(value)
Parameter Values
| Parameter | Description |
|---|---|
value |
Required Any type. The value to remove from the list |
reverse()
Reverses the order of the list
Example
Reverse the order of the animals list:
animals = ['cat', 'dog', 'rabbit', 'hamster']
animals.reverse()
print(animals)
# Output: ['hamster', 'rabbit', 'dog', 'cat']Definition and Usage
The reverse() method reverses the order of the elements in the list. This modifies the original list in place and does not return a new list.
Syntax
list.reverse()
Parameter Values
| Parameter | Description |
|---|---|
| No parameters | |
sort()
Sorts the list in ascending order
Example 1: Basic Sort
Sort the animals list alphabetically:
animals = ['dog', 'cat', 'rabbit', 'hamster']
animals.sort()
print(animals)
# Output: ['cat', 'dog', 'hamster', 'rabbit']Example 2: Sort in Descending Order
Sort the animals list in reverse alphabetical order:
animals = ['dog', 'cat', 'rabbit', 'hamster']
animals.sort(reverse=True)
print(animals)
# Output: ['rabbit', 'hamster', 'dog', 'cat']Example 3: Sort by Length
Sort the animals list by the length of each string:
animals = ['dog', 'cat', 'rabbit', 'hamster']
animals.sort(key=len)
print(animals)
# Output: ['cat', 'dog', 'rabbit', 'hamster']Example 4: Sort by Last Letter
Sort the animals list by the last letter of each string:
def last_letter(s):
return s[-1]
animals = ['dog', 'cat', 'rabbit', 'hamster']
animals.sort(key=last_letter)
print(animals)
# Output: ['rabbit', 'hamster', 'cat', 'dog']Example 5: Sort Dictionaries by Year
Sort a list of dictionaries by year:
animals = [
{'name': 'cat', 'year': 2020},
{'name': 'dog', 'year': 2018},
{'name': 'rabbit', 'year': 2022}
]
animals.sort(key=lambda x: x['year'])
print(animals)
# Output: [{'name': 'dog', 'year': 2018}, {'name': 'cat', 'year': 2020}, {'name': 'rabbit', 'year': 2022}]Example 6: Sort by Age
Sort a list of tuples by age:
animals = [('cat', 5), ('dog', 3), ('rabbit', 2), ('hamster', 4)]
animals.sort(key=lambda x: x[1])
print(animals)
# Output: [('rabbit', 2), ('dog', 3), ('hamster', 4), ('cat', 5)]Example 7: Case-Insensitive Sort
Sort strings in a case-insensitive manner:
animals = ['Dog', 'cat', 'Rabbit', 'hamster']
animals.sort(key=str.lower)
print(animals)
# Output: ['cat', 'Dog', 'hamster', 'Rabbit']Example 8: Sort Numbers by Absolute Value
Sort numbers by their absolute value:
numbers = [5, -3, 8, -1, 2]
numbers.sort(key=abs)
print(numbers)
# Output: [-1, 2, -3, 5, 8]Definition and Usage
The sort() method sorts the list in ascending order by default. This modifies the original list in place and does not return a new list. You can customize the sorting behavior using the reverse and key parameters.
Syntax
list.sort(reverse=True|False, key=myFunc)
Parameter Values
| Parameter | Description |
|---|---|
reverse |
Optional. A Boolean value. False will sort ascending (default), True will sort descending |
key |
Optional. A function to specify the sorting criteria (e.g., len, str.lower, abs, or a custom function) |
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