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The simplicity and power of Python make it the preferred language for many developers. This article will introduce 36 commonly used classic Python code examples. These examples cover basic syntax, common tasks, and some advanced features.

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1. Basic Syntax Cases

Hello World Program

This is the first case when learning any programming language. In Python, you can simply use theprint() function.
The code is as follows:

print("Hello, World!")

The output will displayHello, World! in the console, this case is mainly to familiarize beginners with Python’s basic output statement.

Using Variables

Define variables and perform simple calculations. For example, calculate the sum of two numbers.
The code is as follows:

a = 5
b = 3
sum_result = a + b
print(sum_result)

Here, the variablesa and b are defined, and their sum is assigned to sum_result, with the final output being8. This demonstrates the use of variable definition and basic operations.

Data Type Conversion

For example, convert a string type number to an integer type for calculations.
The code is as follows:

num_str = "10"
num_int = int(num_str)
double_num = num_int * 2
print(double_num)

First, the string"10" is converted to an integer10, then multiplied by2, resulting in an output of20. This case helps understand the importance of data type conversion in Python.

2. String Manipulation Cases

String Concatenation

Join two or more strings together.
The code is as follows:

first_name = "John"
last_name = "Doe"
full_name = first_name + " " + last_name
print(full_name)

The output isJohn Doe, demonstrating how to use the+ operator to concatenate strings.

String Slicing

Extract a substring from a string.
The code is as follows:

text = "Python is great"
sub_text = text[0:6]
print(sub_text)

The output isPython, here[0:6] indicates starting from index0 (inclusive) to index6 (exclusive) for the substring.

String Search and Replace

Find the position of a substring in a string and perform a replacement operation.
The code is as follows:

sentence = "I love Python programming"
find_result = sentence.find("Python")
new_sentence = sentence.replace("Python", "Java")
print(find_result)
print(new_sentence)

find() function returns the starting index position of the substring"Python" (which is7), and thereplace() function replaces"Python" in the string with"Java" and returns the new string.

3. List Manipulation Cases

Creating and Accessing Lists

Create a list and access its elements.
The code is as follows:

fruits = ["apple", "banana", "cherry"]
print(fruits[0])

The output isapple, demonstrating how to create a list and access its elements by index.

Adding and Removing List Elements

Add new elements to the list and remove existing elements.
The code is as follows:

numbers = [1, 2, 3]
numbers.append(4)
print(numbers)
numbers.remove(2)
print(numbers)

append() function adds the element4 to the end of the list, outputting[1, 2, 3, 4], and theremove() function removes the element2 from the list, outputting[1, 3, 4].

Sorting Lists

Sort the elements in the list.
The code is as follows:

unsorted_list = [3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5]
unsorted_list.sort()
print(unsorted_list)

sort() function sorts the listunsorted_list, outputting[1, 1, 2, 3, 3, 4, 5, 5, 5, 6, 9].

4. Loop Structure Cases

For Loop to Traverse a List

Use thefor loop to traverse each element in the list.
The code is as follows:

colors = ["red", "green", "blue"]
for color in colors:    print(color)

This will sequentially outputred, green, and blue, demonstrating the use of thefor loop in traversing iterable objects like lists.

While Loop to Calculate Cumulative Sum

Use thewhile loop to calculate the cumulative sum from 1 to 10.
The code is as follows:

n = 1
sum_value = 0
while n <= 10:    sum_value += n    n += 1
print(sum_value)

Calculating the cumulative sum from 1 to 10, the output is55, reflecting the cumulative operation under the control of thewhile loop.

Nested Loop to Print Multiplication Table

Use nestedfor loops to print the multiplication table.
The code is as follows:

for i in range(1, 10):
    for j in range(1, i + 1):        print(f"{j}*{i}={i*j}", end="\t")    print()

The outer loop controls the number of rows, while the inner loop controls the number of columns in each row. Theend="\t" is used to control the output format, allowing the multiplication table to be neatly arranged.

5. Function Cases

Defining and Calling Simple Functions

Define a function to calculate the product of two numbers and call it.
The code is as follows:

def multiply(a, b):
    return a * b
result = multiply(3, 4)
print(result)

A functionmultiply is defined, which takes two parametersa and b and returns their product. Calling the functionmultiply(3, 4) outputs12.

Default Parameters in Functions

Set default parameters when defining functions for convenient calls.
The code is as follows:

def greet(name = "World"):
    print(f"Hello, {name}!")
greet()
greet("Alice")

The functiongreet has a default parametername with a default value of"World". When called without passing a parameter, it outputsHello, World!, and when passing the parameter"Alice", it outputsHello, Alice!.

Recursive Function Calls

For example, calculate factorial to demonstrate recursive function calls.
The code is as follows:

def factorial(n):
    if n == 0 or n == 1:        return 1    else:        return n * factorial(n - 1)
print(factorial(5))

Calculating the factorial of5, the functionfactorial will call itself untiln equals0 or1, outputting120.

6. File Operation Cases

Reading Files

Read the contents of a text file and print it.
The code is as follows:

with open("test.txt", "r") as file:
    content = file.read()    print(content)

Assuming thetest.txt file exists, thewith statement will automatically manage the opening and closing of the file, and theread() function reads all the content of the file and prints it.

Writing to Files

Write content to a file.
The code is as follows:

with open("output.txt", "w") as file:
    file.write("This is a test.")

Open theoutput.txt file (creating it if it doesn’t exist), using thewrite() function to writeThis is a test.. Note that thew mode will overwrite the existing content of the file.

Appending to Files

Append content to the end of a file.
The code is as follows:

with open("output.txt", "a") as file:
    file.write("\nAppend this line.")

Open theoutput.txt file ina (append) mode, adding the lineAppend this line. at the end of the file.

7. Module and Package Cases

Creating and Using Custom Modules

Create a simple module containing a function, and then use this module in another Python file.
Assuming you create a module namedmy_module.py, with the following content:

def add_numbers(a, b):
    return a + b

Use this module in another file:

import my_module
result = my_module.add_numbers(3, 4)
print(result)

First import themy_module module, then call theadd_numbers function, outputting7.

Using Standard Library Modules (e.g. math)

Use themath module for mathematical calculations, such as calculating square roots.
The code is as follows:

import math
number = 9
square_root = math.sqrt(number)
print(square_root)

After importing themath module, use thesqrt function to calculate the square root of9, outputting3.

Creating and Using Python Packages

Create a Python package containing multiple modules, and use this package in other programs.
Assuming you create a package namedmy_package, which containsmodule1.py and module2.py two modules.
Inmodule1.py there is a functionfunction1, and inmodule2.py there is a functionfunction2.
To use this package, you need to properly import the modules in the__init__.py file (the package initialization file) (for example,from . import module1 and from . import module2).
Then in other files you can use it like this:

from my_package import module1, module2
result1 = module1.function1()
result2 = module2.function2()
print(result1)
print(result2)

8. Object-Oriented Programming Cases

Defining Classes and Creating Objects

Define a simple class with properties and methods, then create objects.
The code is as follows:

class Dog:
    def __init__(self, name, age):        self.name = name        self.age = age
    def bark(self):        print(f"{self.name} says Woof!")
my_dog = Dog("Buddy", 3)
print(my_dog.name)
my_dog.bark()

Defined theDog class with two propertiesname and age, and thebark method prints the dog’s barking message. Created an objectmy_dog of theDog class, accessed the object’s propertyname and called thebark method.

Class Inheritance

Define a subclass that inherits from a parent class and overrides a method.
The code is as follows:

class Animal:
    def move(self):        print("Animal is moving.")
class Cat(Animal):
    def move(self):        print("Cat is running.")
my_cat = Cat()
my_cat.move()

Defined theAnimal class and theCat class inheriting from it, where theCat class overrides themove method of theAnimal class. Created an objectmy_cat of theCat class and called themove method, outputtingCat is running..

Demonstrating Polymorphism

Using polymorphism, different objects call the same method name to produce different behaviors.
The code is as follows:

class Bird:
    def fly(self):        print("Bird is flying.")
class Plane:
    def fly(self):        print("Plane is flying.")
def make_fly(obj):    obj.fly()
bird = Bird()
plane = Plane()
make_fly(bird)
make_fly(plane)

Defined theBird class and thePlane class, both having afly method. The functionmake_fly accepts an object and calls itsfly method. By passingBird andPlane objects, polymorphism is demonstrated.

9. Data Structure Cases (Dictionaries, Sets)

Creating and Accessing Dictionaries

Create a dictionary and access corresponding values by keys.
The code is as follows:

student = {"name": "Tom", "age": 20, "major": "Computer Science"}
print(student["name"])

The output isTom, demonstrating how to create a dictionary and use keys to retrieve corresponding values.

Adding and Deleting Key-Value Pairs in Dictionaries

Add new key-value pairs to the dictionary and delete existing ones.
The code is as follows:

car = {"brand": "Toyota", "model": "Corolla"}
car["color"] = "Blue"
print(car)
del car["model"]
print(car)

First, add the key-value pair"color": "Blue", outputting{"brand": "Toyota", "model": "Corolla", "color": "Blue"}, then delete the key-value pair"model", outputting{"brand": "Toyota", "color": "Blue"}.

Creating Sets and Basic Operations (Intersection, Union)

Create sets and perform intersection and union operations.
The code is as follows:

set1 = {1, 2, 3, 4}
set2 = {3, 4, 5, 6}
intersection_result = set1 & set2
union_result = set1 | set2
print(intersection_result)
print(union_result)

& operator is used for intersection, outputting{3, 4}, and| operator is used for union, outputting{1, 2, 3, 4, 5, 6}.

10. Exception Handling Cases

Simple Exception Handling (e.g., Division by Zero)

Catch division by zero exceptions to prevent program crashes.
The code is as follows:

try:
    result = 5 / 0
except ZeroDivisionError:    print("Cannot divide by zero")

When executing5/0, aZeroDivisionError exception will be raised, and theexcept block will catch this exception and printCannot divide by zero, instead of crashing the program.

Handling Multiple Exceptions

Handle multiple different types of exceptions simultaneously.
The code is as follows:

try:
    num_str = "abc"
    num = int(num_str)
    result = 10 / num
except ValueError:    print("Cannot convert string to integer")
except ZeroDivisionError:    print("Cannot divide by zero")

Here, there may be two types of exceptions, one is theValueError when converting a non-numeric string to an integer, and the other is possible division by zeroZeroDivisionError. Execute the correspondingexcept block according to the different exception types.

Raising Exceptions (raise)

Proactively raise exceptions under specific conditions.
The code is as follows:

def divide(a, b):
    if b == 0:        raise ZeroDivisionError("The divisor cannot be zero")    return a / b
try:    result = divide(5, 0)
except ZeroDivisionError as e:    print(e)

The functiondivide proactively raises aZeroDivisionError exception whenb is0, caught in thetry - except block and prints the exception message.

11. Network Programming Cases (Simple TCP Communication)

Setting Up a Simple TCP Server

Create a simple TCP server that listens on a port and accepts client connections.
The code is as follows:

import socket
server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
server_address = ('localhost', 8888)
server_socket.bind(server_address)
server_socket.listen(1)
print("Server is listening on port 8888...")

As the saying goes:Reading a hundred times is not as good as practicing!

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100 Classic Python Programming Cases with Source Code

As the saying goes:Reading a hundred times is not as good as practicing!

Many students face this situation: they have learned a lot of theoretical knowledge, but when it comes to hands-on practice, they become confused and don’t know how to start.

Today, I have selected 23 Python project development cases (full-color HD PDF share) for you to use immediately! Covering8 development directions, 23 projects, gradually allowing readers to learn through practice and improve their actual development capabilities.

Directory

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As the saying goes:Reading a hundred times is not as good as practicing!

Many students face this situation: they have learned a lot of theoretical knowledge, but when it comes to hands-on practice, they become confused and don’t know how to start.

Today, I have selected 23 Python project development cases (full-color HD PDF share) for you to use immediately! Covering8 development directions, 23 projects, gradually allowing readers to learn through practice and improve their actual development capabilities.

Directory

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