Comprehensive Python Basics: Variables, Data Types, Control Structures, Functions, OOP, Standard Library, and More

This guide introduces Python programming fundamentals in a structured manner.

1. Variables and Data Types – Variables store data, and assignment uses the = operator. Example definitions include integers, floats, strings, booleans, lists, tuples, dictionaries, and sets:

变量：用于存储数据的标识符。 赋值：使用 = 运算符将值赋给变量。 x = 10 # 整数 y = 3.14 # 浮点数 name = "Alice" # 字符串 is_student = True # 布尔值

Additional examples for each type:

x = 10 y = -5 z = 0

pi = 3.14159 temperature = 23.5

name = "Alice" message = 'Hello, world!' greeting = f"Hello, {name}!" # f-string

is_student = True is_teacher = False

fruits = ["apple", "banana", "cherry"] numbers = [1, 2, 3, 4, 5] mixed_list = [1, "two", 3.0, True]

coordinates = (10, 20) colors = ("red", "green", "blue")

person = {"name": "Bob", "age": 30, "city": "New York"} settings = {"theme": "dark", "language": "en"}

unique_numbers = {1, 2, 3, 4, 5} vowels = {'a', 'e', 'i', 'o', 'u'}

2. Control Structures – Conditional statements and loops control program flow.

x = 10 if x > 0: print("x is positive") elif x == 0: print("x is zero") else: print("x is negative")

fruits = ["apple", "banana", "cherry"] for fruit in fruits: print(fruit) for i in range(5): # 0, 1, 2, 3, 4 print(i)

count = 0 while count < 5: print(count) count += 1

3. Functions – Define reusable blocks with def , accept parameters, and return values.

def greet(name): return f"Hello, {name}!" print(greet("Alice")) # 输出: Hello, Alice!

def add(a, b): return a + b def greet_with_message(name, message="Hello"): return f"{message}, {name}!" def multiply(*args): result = 1 for num in args: result *= num return result def print_info(**kwargs): for key, value in kwargs.items(): print(f"{key}: {value}") print(add(3, 5)) # 输出: 8 print(greet_with_message("Alice")) # 输出: Hello, Alice! print(greet_with_message("Bob", "Hi")) # 输出: Hi, Bob! print(multiply(2, 3, 4)) # 输出: 24 print_info(name="Alice", age=30, city="New York")

4. Classes and Objects – Object‑oriented programming with classes, inheritance, methods, and attributes.

class Person: def __init__(self, name, age): self.name = name self.age = age def display(self): print(f"Name: {self.name}, Age: {self.age}") person = Person("Alice", 30) person.display() # 输出: Name: Alice, Age: 30

class Student(Person): def __init__(self, name, age, grade): super().__init__(name, age) self.grade = grade def study(self): print(f"{self.name} is studying.") student = Student("Bob", 20, "Sophomore") student.display() # 输出: Name: Bob, Age: 20 student.study() # 输出: Bob is studying.

5. Standard Library – Common modules for OS interaction, system info, dates, math, and randomness.

import os current_directory = os.getcwd() print(f"Current directory: {current_directory}") files = os.listdir(current_directory) print(f"Files in the directory: {files}")

import sys print(f"Python version: {sys.version}") print(f"Platform: {sys.platform}") print(f"Command-line arguments: {sys.argv}")

from datetime import datetime now = datetime.now() print(f"Current date and time: {now}") formatted_date = now.strftime("%Y-%m-%d %H:%M:%S") print(f"Formatted date and time: {formatted_date}")

import math sqrt_value = math.sqrt(16) print(f"Square root of 16: {sqrt_value}") pi_value = math.pi print(f"Value of pi: {pi_value}")

import random random_number = random.randint(1, 100) print(f"Random number between 1 and 100: {random_number}") random_float = random.random() print(f"Random float between 0 and 1: {random_float}")

6. File Operations – Reading, writing, and appending files using open .

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

with open('file.txt', 'r') as file: for line in file: print(line.strip())

with open('output.txt', 'w') as file: file.write("Hello, World!\n") file.write("This is a new line.\n")

with open('output.txt', 'a') as file: file.write("This is an appended line.\n")

7. Exception Handling – Managing errors with try , except , finally , and raise .

try: result = 10 / 0 except ZeroDivisionError as e: print(f"Error: {e}")

try: x = int(input("Enter a number: ")) y = 10 / x except ValueError: print("Invalid input. Please enter a number.") except ZeroDivisionError: print("Cannot divide by zero.")

try: file = open('file.txt', 'r') content = file.read() print(content) except FileNotFoundError: print("File not found.") finally: file.close()

def validate_age(age): if age < 0: raise ValueError("Age cannot be negative.") return age try: age = validate_age(-5) except ValueError as e: print(e)

8. List Comprehensions – Concise list creation.

squares = [x**2 for x in range(10)] print(squares) # 输出: [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

even_squares = [x**2 for x in range(10) if x % 2 == 0] print(even_squares) # 输出: [0, 4, 16, 36, 64]

9. Dictionary Comprehensions – Concise dictionary creation.

squares_dict = {x: x**2 for x in range(10)} print(squares_dict) # 输出: {0: 0, 1: 1, 2: 4, 3: 9, 4: 16, 5: 25, 6: 36, 7: 49, 8: 64, 9: 81}

even_squares_dict = {x: x**2 for x in range(10) if x % 2 == 0} print(even_squares_dict) # 输出: {0: 0, 2: 4, 4: 16, 6: 36, 8: 64}

10. Generator Expressions – Lazy evaluation of sequences.

squares_gen = (x**2 for x in range(10)) for square in squares_gen: print(square)

11. Decorators – Modify or extend function behavior.

def my_decorator(func): def wrapper(): print("Something is happening before the function is called.") func() print("Something is happening after the function is called.") return wrapper @my_decorator def say_hello(): print("Hello!") say_hello()

def repeat(num_times): def decorator(func): def wrapper(*args, **kwargs): for _ in range(num_times): result = func(*args, **kwargs) return result return wrapper return decorator @repeat(3) def greet(name): print(f"Hello, {name}!") greet("Alice")

12. Modules and Packages – Organize code into reusable units.

# my_module.py def greet(name): return f"Hello, {name}!" # main.py import my_module print(my_module.greet("Alice"))

# my_package/ # ├── __init__.py # ├── module1.py # └── module2.py # module1.py def add(a, b): return a + b # module2.py def subtract(a, b): return a - b # main.py from my_package.module1 import add from my_package.module2 import subtract print(add(3, 5)) # 输出: 8 print(subtract(10, 5)) # 输出: 5

13. Virtual Environments – Isolate project dependencies.

python -m venv myenv source myenv/bin/activate # macOS/Linux myenv\Scripts\activate # Windows

pip install requests pip freeze > requirements.txt # 生成依赖文件 pip install -r requirements.txt # 安装依赖

14. Code Style (PEP 8) – Follow Python’s official style guide.

def calculate_area(length, width): """ Calculate the area of a rectangle. """ return length * width

15. Version Control (Git) – Track changes and collaborate.

git init git add . git commit -m "Initial commit" git remote add origin https://github.com/yourusername/yourrepo.git git push -u origin master