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!
")
    file.write("This is a new line.
")

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

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