Python Basics: Dictionaries, Sets, File Operations, Regular Expressions, Logging, Unit Testing, Profiling, and Third‑Party Libraries

Dictionary (dict)

A dictionary stores key‑value pairs, making it ideal for data storage and retrieval.

# 创建字典：
person = {"name": "Alice", "age": 25, "city": "New York"}
print(person["name"])  # 输出: Alice
print(person.get("name"))  # 输出: Alice
person["email"] = "[email protected]"  # 添加新元素
person["age"] = 26  # 修改现有元素
del person["city"]  # 删除元素
for key, value in person.items():
    print(f"{key}: {value}")

Set (set)

A set is an unordered collection of unique items, useful for deduplication and set operations.

# 创建集合：
numbers = {1, 2, 3, 4}
numbers.add(5)  # 添加元素
numbers.remove(3)  # 删除元素
set1 = {1, 2, 3}
set2 = {3, 4, 5}
union = set1 | set2  # 并集
intersection = set1 & set2  # 交集
difference = set1 - set2  # 差集
symmetric_difference = set1 ^ set2  # 对称差集

File and Directory Operations

Python’s os module provides functions for working with files and directories.

# 导入 os 模块：
import os
current_dir = os.getcwd()
print(current_dir)
os.chdir("/path/to/new/directory")
os.mkdir("/path/to/new/directory")
os.rmdir("/path/to/directory")
files = os.listdir("/path/to/directory")
print(files)
# 路径拼接
path = os.path.join("/home/user", "data", "file.txt")
print(path)
if os.path.exists("/path/to/file.txt"):
    print("File exists")
else:
    print("File does not exist")
size = os.path.getsize("/path/to/file.txt")
print(size)

Regular Expressions

Regular expressions enable powerful pattern matching and text manipulation.

# 导入 re 模块
import re
pattern = r"\d+"  # 匹配一个或多个数字
text = "The price is 100 dollars."
match = re.search(pattern, text)
if match:
    print(match.group())  # 输出: 100
new_text = re.sub(r"\d+", "XXX", text)
print(new_text)  # 输出: The price is XXX dollars.
matches = re.findall(r"\d+", text)
print(matches)  # 输出: ['100']

Logging

Logging helps track program execution and errors.

# 导入 logging 模块
import logging
logging.basicConfig(level=logging.DEBUG,
                    format='%(asctime)s - %(levelname)s - %(message)s')
logging.debug("This is a debug message")
logging.info("This is an info message")
logging.warning("This is a warning message")
logging.error("This is an error message")
logging.critical("This is a critical message")
# 输出到文件
logging.basicConfig(filename='app.log', level=logging.DEBUG,
                    format='%(asctime)s - %(levelname)s - %(message)s')

Unit Testing

Python’s unittest module simplifies writing and running tests.

# 导入 unittest 模块
import unittest
class TestAddition(unittest.TestCase):
    def test_add(self):
        self.assertEqual(add(1, 2), 3)
    def test_add_negative(self):
        self.assertEqual(add(-1, -2), -3)
if __name__ == '__main__':
    unittest.main()

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

Performance Profiling

Profiling identifies bottlenecks; cProfile is the standard tool.

# 导入 cProfile 模块
import cProfile

def example_function():
    # Your code here
    pass
cProfile.run('example_function()')

Third‑Party Libraries

Python’s ecosystem offers many libraries to extend functionality.

# 使用 pip 安装库：
pip install requests
pip install beautifulsoup4
# 使用 requests 发送 HTTP 请求
import requests
response = requests.get("https://api.example.com/data")
print(response.status_code)
print(response.json())
# 使用 beautifulsoup4 解析 HTML
from bs4 import BeautifulSoup
import requests
response = requests.get("https://www.example.com")
soup = BeautifulSoup(response.text, 'html.parser')
print(soup.title.string)