PythonLists in Python
- Introduction to lists
- What are lists
- how to create a list
- accessing list elements
- basic list operations
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List comprehension
- Syntax
- examples
- use cases of this powerful tool for creating lists in a concise
- readable way
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Nested lists
- Creating and working with lists that contain other lists as elements.
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List slicing
- Syntax and examples of slicing a list to create a new list with a subset of its elements
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Modifying lists
- Adding elements in a list
- removing elements in a list
- modifying elements in a list
- implications of mutable objects
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Copying and cloning lists
- Creating a shallow or deep copy of a list using slicing
- the copy() method
- the list() constructor
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Iterating over lists
- Using a for loop to traverse a list
- the built-in function enumerate() for getting both the index and value of each element
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List operations
- Concatenating two or more lists using the + operator
- repeating a list using the * operator
- comparing lists using the == and != operators
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Common errors and pitfalls
- Common mistakes that beginners make when working with lists and how to avoid or fix them
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Some More topics:
- list unpacking
- generator expressions
- using the bisect module for efficient insertion in a sorted list
List of Methods in Python
| Method Name | Description |
|---|---|
| append() | Adds an element to the end of a list |
| clear() | Removes all elements from a list |
| count() | Returns the number of times a specified element appears in a list |
| extend() | Adds the elements of one list to the end of another list |
| index() | Returns the index of the first element with the specified value |
| insert() | Adds an element at the specified position |
| pop() | Removes and returns the element at the specified position |
| remove() | Removes the first element with the specified value |
| reverse() | Reverses the order of the elements in a list |
| sort() | Sorts the elements of a list in ascending order |
| copy() | Returns a shallow copy of the list. |
| class() | Returns the class of an object. |
| contains() | Used to check if an element is in a container (such as a list, tuple, or set). |
| delattr() | Used to delete an attribute of an object. |
| dir() | Returns a list of attributes and methods of an object. |
| doc() | Returns the documentation string of an object. |
| eq() | Used to check if two objects are equal. |
| format() | Used to format a string. |
| ge() | Used to check if one object is greater than or equal to another. |
| getattribute() | Used to get the value of an attribute of an object. |
| getitem() | Used to get an element from a container (such as a list or tuple). |
| gt() | Used to check if one object is greater than another. |
| hash() | Returns the hash value of an object. |
| iadd() | Used to add another object to an object in place. |
| imul() | Used to multiply an object by another object in place. |
| init() | Used to initialize an object. |
| init_subclass() | Used to customize the behavior of subclass creation. |
| iter() | Returns an iterator for an object. |
| le() | Used to check if one object is less than or equal to another. |
| len() | Returns the length of an object. |
| lt() | Used to check if one object is less than another. |
| mul() | Used to multiply an object by another object. |
| ne() | Used to check if two objects are not equal. |
| new() | Used to create a new instance of a class. |
| reduce() | Used to apply a function to a sequence of elements to reduce it to a single value. |
| reduce_ex() | Similar to reduce(), but with additional error handling capabilities. |
| repr() | Returns a string representation of an object. |
| reversed() | Returns a reverse iterator for a sequence. |
| rmul() | Used to multiply another object by an object. |
| setattr() | Used to set the value of an attribute of an object. |
| setitem() | Used to set the value of an element in a container (such as a list or tuple). |
| sizeof() | Returns the size of an object in bytes. |
my_list = [1, 2, 3, 4, 5]
print(my_list) # prints [1, 2, 3, 4, 5]
You can access individual items in a list using their index, which starts at 0:
my_list = [1, 2, 3, 4, 5]
print(my_list[0]) # prints 1
print(my_list[3]) # prints 4
You can also use negative indexing to access items from the end of the list:
my_list = [1, 2, 3, 4, 5]
print(my_list[-1]) # prints 5
print(my_list[-3]) # prints 3
You can modify items in a list by accessing them directly using their index:
my_list = [1, 2, 3, 4, 5]
my_list[2] = 10
print(my_list) # prints [1, 2, 10, 4, 5]
You can add items to a list using the append() method:
my_list = [1, 2, 3, 4, 5]
my_list.append(6)
print(my_list) # prints [1, 2, 3, 4, 5, 6]
You can remove items from a list using the remove() method:
my_list = [1, 2, 3, 4, 5]
my_list.remove(3)
print(my_list) # prints [1, 2, 4, 5]
You can also use the del keyword to remove items from a list:
my_list = [1, 2, 3, 4, 5]
del my_list[2]
print(my_list) # prints [1, 2, 4, 5]
You can get the length of a list using the len() function:
my_list = [1, 2, 3, 4, 5]
print(len(my_list)) # prints 5
You can also use slicing to get a subset of a list:
my_list = [1, 2, 3, 4, 5]
print(my_list[1:3]) # prints [2, 3]
print(my_list[:2]) # prints [1, 2]
print(my_list[3:]) # prints [4, 5]
print(my_list[:]) # prints [1, 2, 3, 4, 5]
You can concatenate two lists using the + operator:
list1 = [1, 2, 3]
list2 = [4, 5, 6]
concatenated_list = list1 + list2
print(concatenated_list) # prints [1, 2, 3, 4, 5, 6]
You can also use the * operator to repeat a list:
my_list = [1, 2, 3]
repeated_list = my_list * 3
print(repeated_list) # prints [1, 2, 3, 1, 2, 3, 1, 2, 3]
Lists are mutable, which means you can modify them in place. This is different from tuples, which are immutable:
my_list = [1, 2, 3]
my_tuple = (1, 2, 3)
my_list[0] = 10
# my_tuple[0] = 10 # raises TypeError
print(my_list) # prints [10, 2, 3]
print(my_tuple) # prints (1, 2, 3)
Lists can also be nested, meaning that you can have lists inside of other lists:
nested_list = [[1, 2], [3, 4], [5, 6]]
print(nested_list[0]) # prints [1, 2]
print(nested_list[1][0]) # prints 3
Finally, you can use list comprehension to create new lists based on existing lists:
my_list = [1, 2, 3, 4, 5]
new_list = [x * 2 for x in my_list if x % 2 == 0]
print(new_list) # prints [4, 8]
That's a brief introduction to lists in Python!