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

Dictionaries (dict) : A key‑value data structure ideal for storing and retrieving data.

person = {"name": "Alice", "age": 25, "city": "New York"}
print(person["name"])  # Alice
print(person.get("name"))  # Alice
person["email"] = "[email protected]"  # add
person["age"] = 26  # modify
del person["city"]  # delete
for key, value in person.items():
    print(f"{key}: {value}")

Sets (set) : An unordered collection of unique items, useful for deduplication and set operations.

numbers = {1, 2, 3, 4}
numbers.add(5)      # add element
numbers.remove(3)   # remove element
set1 = {1, 2, 3}
set2 = {3, 4, 5}
union = set1 | set2            # {1, 2, 3, 4, 5}
intersection = set1 & set2     # {3}
difference = set1 - set2       # {1, 2}
symmetric_difference = set1 ^ set2  # {1, 2, 4, 5}

File and Directory Operations : Using the os module to manipulate paths, directories, and files.

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)
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 : Powerful pattern matching with the re module.

import re
pattern = r"\d+"
text = "The price is 100 dollars."
match = re.search(pattern, text)
if match:
    print(match.group())  # 100
new_text = re.sub(r"\d+", "XXX", text)
print(new_text)  # The price is XXX dollars.
matches = re.findall(r"\d+", text)
print(matches)  # ['100']

Logging : Configuring and using the logging module for console and file output.

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")
# Log to a file
logging.basicConfig(filename='app.log', level=logging.DEBUG,
                    format='%(asctime)s - %(levelname)s - %(message)s')

Unit Testing : Writing tests with the built‑in unittest framework.

import unittest

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

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()

Performance Profiling : Using cProfile to identify bottlenecks.

import cProfile

def example_function():
    # Your code here
    pass

cProfile.run('example_function()')

Third‑Party Libraries : Installing with pip and using popular packages like requests and beautifulsoup4 .

# Install libraries
pip install requests
pip install beautifulsoup4

# Use requests
import requests
response = requests.get("https://api.example.com/data")
print(response.status_code)
print(response.json())

# Parse HTML with BeautifulSoup
from bs4 import BeautifulSoup
response = requests.get("https://www.example.com")
soup = BeautifulSoup(response.text, 'html.parser')
print(soup.title.string)