Python Lists Explained: A Beginner’s Guide with Examples

Python lists are one of the most fundamental and versatile data structures in programming. They allow you to store and manage collections of data efficiently. In this article, we’ll dive into what lists are, how to use them, and some common operations and examples.

What is a Python List?

A list in Python is an ordered collection of elements, enclosed in square brackets []. Lists can contain elements of different types, such as integers, strings, floats, or even other lists. The best part? Lists are mutable, meaning their contents can be modified.

<span># Example of a list with integers </span><span>numbers</span> <span>=</span> <span>[</span><span>1</span><span>,</span> <span>2</span><span>,</span> <span>3</span><span>,</span> <span>4</span><span>,</span> <span>5</span><span>]</span>
<span># Example of a list with mixed data types </span><span>mixed_list</span> <span>=</span> <span>[</span><span>1</span><span>,</span> <span>"</span><span>hello</span><span>"</span><span>,</span> <span>3.14</span><span>,</span> <span>True</span><span>]</span>
<span># Example of a list with integers </span><span>numbers</span> <span>=</span> <span>[</span><span>1</span><span>,</span> <span>2</span><span>,</span> <span>3</span><span>,</span> <span>4</span><span>,</span> <span>5</span><span>]</span>

<span># Example of a list with mixed data types </span><span>mixed_list</span> <span>=</span> <span>[</span><span>1</span><span>,</span> <span>"</span><span>hello</span><span>"</span><span>,</span> <span>3.14</span><span>,</span> <span>True</span><span>]</span>
# Example of a list with integers numbers = [1, 2, 3, 4, 5]

# Example of a list with mixed data types mixed_list = [1, "hello", 3.14, True]

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How to Access List Elements

You can access elements of a list by using their index. Python uses zero-based indexing, meaning the first element is accessed with an index of 0.

<span>print</span><span>(</span><span>numbers</span><span>[</span><span>0</span><span>])</span>  <span># Output: 1 </span><span>print</span><span>(</span><span>mixed_list</span><span>[</span><span>1</span><span>])</span>  <span># Output: "hello" </span>
<span>print</span><span>(</span><span>numbers</span><span>[</span><span>0</span><span>])</span>  <span># Output: 1 </span><span>print</span><span>(</span><span>mixed_list</span><span>[</span><span>1</span><span>])</span>  <span># Output: "hello" </span>
print(numbers[0])  # Output: 1 print(mixed_list[1])  # Output: "hello" 

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Modifying List Elements

Since lists are mutable, you can modify an element at a specific index:

<span>numbers</span><span>[</span><span>2</span><span>]</span> <span>=</span> <span>10</span>
<span>print</span><span>(</span><span>numbers</span><span>)</span>  <span># Output: [1, 2, 10, 4, 5] </span>
<span>numbers</span><span>[</span><span>2</span><span>]</span> <span>=</span> <span>10</span>
<span>print</span><span>(</span><span>numbers</span><span>)</span>  <span># Output: [1, 2, 10, 4, 5] </span>
numbers[2] = 10
print(numbers)  # Output: [1, 2, 10, 4, 5] 

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Adding Elements to a List

You can easily add elements to a list using methods like append() and insert():

<span># Using append to add an element to the end </span><span>numbers</span><span>.</span><span>append</span><span>(</span><span>6</span><span>)</span>
<span>print</span><span>(</span><span>numbers</span><span>)</span>  <span># Output: [1, 2, 10, 4, 5, 6] </span>
<span># Using insert to add an element at a specific index </span><span>numbers</span><span>.</span><span>insert</span><span>(</span><span>1</span><span>,</span> <span>20</span><span>)</span>
<span>print</span><span>(</span><span>numbers</span><span>)</span>  <span># Output: [1, 20, 2, 10, 4, 5, 6] </span>
<span># Using append to add an element to the end </span><span>numbers</span><span>.</span><span>append</span><span>(</span><span>6</span><span>)</span>
<span>print</span><span>(</span><span>numbers</span><span>)</span>  <span># Output: [1, 2, 10, 4, 5, 6] </span>
<span># Using insert to add an element at a specific index </span><span>numbers</span><span>.</span><span>insert</span><span>(</span><span>1</span><span>,</span> <span>20</span><span>)</span>
<span>print</span><span>(</span><span>numbers</span><span>)</span>  <span># Output: [1, 20, 2, 10, 4, 5, 6] </span>
# Using append to add an element to the end numbers.append(6)
print(numbers)  # Output: [1, 2, 10, 4, 5, 6] 
# Using insert to add an element at a specific index numbers.insert(1, 20)
print(numbers)  # Output: [1, 20, 2, 10, 4, 5, 6] 

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Removing Elements from a List

Python provides several ways to remove elements from a list:

• remove(): Removes the first occurrence of a specified value.
• pop(): Removes the last element or the element at a specified index.
• del: Deletes an element at a specified index.

<span>numbers</span><span>.</span><span>remove</span><span>(</span><span>20</span><span>)</span>
<span>print</span><span>(</span><span>numbers</span><span>)</span>  <span># Output: [1, 2, 10, 4, 5, 6] </span>
<span>numbers</span><span>.</span><span>pop</span><span>(</span><span>2</span><span>)</span>  <span># Removes element at index 2 </span><span>print</span><span>(</span><span>numbers</span><span>)</span>  <span># Output: [1, 2, 4, 5] </span>
<span>del</span> <span>numbers</span><span>[</span><span>1</span><span>]</span>  <span># Deletes element at index 1 </span><span>print</span><span>(</span><span>numbers</span><span>)</span>  <span># Output: [1, 4, 5] </span>
<span>numbers</span><span>.</span><span>remove</span><span>(</span><span>20</span><span>)</span>
<span>print</span><span>(</span><span>numbers</span><span>)</span>  <span># Output: [1, 2, 10, 4, 5, 6] </span>
<span>numbers</span><span>.</span><span>pop</span><span>(</span><span>2</span><span>)</span>  <span># Removes element at index 2 </span><span>print</span><span>(</span><span>numbers</span><span>)</span>  <span># Output: [1, 2, 4, 5] </span>
<span>del</span> <span>numbers</span><span>[</span><span>1</span><span>]</span>  <span># Deletes element at index 1 </span><span>print</span><span>(</span><span>numbers</span><span>)</span>  <span># Output: [1, 4, 5] </span>
numbers.remove(20)
print(numbers)  # Output: [1, 2, 10, 4, 5, 6] 
numbers.pop(2)  # Removes element at index 2 print(numbers)  # Output: [1, 2, 4, 5] 
del numbers[1]  # Deletes element at index 1 print(numbers)  # Output: [1, 4, 5] 

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Slicing a List

You can create a sublist from a list using slicing:

<span>subset</span> <span>=</span> <span>numbers</span><span>[</span><span>1</span><span>:</span><span>3</span><span>]</span>
<span>print</span><span>(</span><span>subset</span><span>)</span>  <span># Output: [4, 5] </span>
<span>subset</span> <span>=</span> <span>numbers</span><span>[</span><span>1</span><span>:</span><span>3</span><span>]</span>
<span>print</span><span>(</span><span>subset</span><span>)</span>  <span># Output: [4, 5] </span>
subset = numbers[1:3]
print(subset)  # Output: [4, 5] 

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List Comprehension

List comprehension offers a concise way to create lists:

<span>doubled</span> <span>=</span> <span>[</span><span>x</span> <span>*</span> <span>2</span> <span>for</span> <span>x</span> <span>in</span> <span>numbers</span><span>]</span>
<span>print</span><span>(</span><span>doubled</span><span>)</span>  <span># Output: [2, 8, 10] </span>
<span>doubled</span> <span>=</span> <span>[</span><span>x</span> <span>*</span> <span>2</span> <span>for</span> <span>x</span> <span>in</span> <span>numbers</span><span>]</span>
<span>print</span><span>(</span><span>doubled</span><span>)</span>  <span># Output: [2, 8, 10] </span>
doubled = [x * 2 for x in numbers]
print(doubled)  # Output: [2, 8, 10] 

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Checking for Element Existence

You can check if an item exists in a list using the in keyword:

<span>print</span><span>(</span><span>4</span> <span>in</span> <span>numbers</span><span>)</span>  <span># Output: True </span>
<span>print</span><span>(</span><span>4</span> <span>in</span> <span>numbers</span><span>)</span>  <span># Output: True </span>
print(4 in numbers)  # Output: True 

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Common List Methods

• len(list): Returns the number of elements.
• sort(): Sorts the list in place.
• reverse(): Reverses the list in place.

<span>numbers</span> <span>=</span> <span>[</span><span>3</span><span>,</span> <span>1</span><span>,</span> <span>4</span><span>,</span> <span>1</span><span>,</span> <span>5</span><span>,</span> <span>9</span><span>]</span>
<span>numbers</span><span>.</span><span>sort</span><span>()</span>
<span>print</span><span>(</span><span>numbers</span><span>)</span>  <span># Output: [1, 1, 3, 4, 5, 9] </span>
<span>numbers</span><span>.</span><span>reverse</span><span>()</span>
<span>print</span><span>(</span><span>numbers</span><span>)</span>  <span># Output: [9, 5, 4, 3, 1, 1] </span>
<span>print</span><span>(</span><span>len</span><span>(</span><span>numbers</span><span>))</span>  <span># Output: 6 </span>
<span>numbers</span> <span>=</span> <span>[</span><span>3</span><span>,</span> <span>1</span><span>,</span> <span>4</span><span>,</span> <span>1</span><span>,</span> <span>5</span><span>,</span> <span>9</span><span>]</span>
<span>numbers</span><span>.</span><span>sort</span><span>()</span>
<span>print</span><span>(</span><span>numbers</span><span>)</span>  <span># Output: [1, 1, 3, 4, 5, 9] </span>
<span>numbers</span><span>.</span><span>reverse</span><span>()</span>
<span>print</span><span>(</span><span>numbers</span><span>)</span>  <span># Output: [9, 5, 4, 3, 1, 1] </span>
<span>print</span><span>(</span><span>len</span><span>(</span><span>numbers</span><span>))</span>  <span># Output: 6 </span>
numbers = [3, 1, 4, 1, 5, 9]
numbers.sort()
print(numbers)  # Output: [1, 1, 3, 4, 5, 9] 
numbers.reverse()
print(numbers)  # Output: [9, 5, 4, 3, 1, 1] 
print(len(numbers))  # Output: 6 

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Conclusion

Python lists are a powerful tool for managing collections of data. Whether you need to store numbers, strings, or more complex objects, lists provide the flexibility and functionality to meet your needs. From adding, removing, and modifying elements to slicing and using list comprehension, there are countless ways to work with lists in Python.

With the examples and tips provided, you should now have a solid understanding of how to create and manipulate lists effectively in Python.

原文链接：Python Lists Explained: A Beginner’s Guide with Examples