# Python

This guide quickly references essential Python syntax, functions, and concepts. Whether you are a beginner or an experienced developer, this cheat sheet will help you improve your Python skills. You'll find examples of basic syntax, data structures, control flow, functions, classes, and more. 

### Basic Syntax

#### Variables

```python
x = 10
y = "Hello, World!"
z = 3.14
```

#### Data Types

```python
integer = 10
floating_point = 3.14
string = "Hello"
boolean = True
list = [1, 2, 3]
dictionary = {"key": "value"}
tuple = (1, 2, 3)
set = {1, 2, 3}
```

#### Control Structures

**Conditional Statements**

```python
if x > 5:
    print("x is greater than 5")
elif x == 5:
    print("x is 5")
else:
    print("x is less than 5")
```

**Loops**

```python
for i in range(5):
    print(i)

while x > 0:
    print(x)
    x -= 1
```

#### Functions

```python
def greet(name):
    return f"Hello, {name}!"

print(greet("Alice"))
```

#### Classes

```python
class Dog:
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def bark(self):
        return f"{self.name} says woof!"

dog = Dog("Buddy", 3)
print(dog.bark())
```

#### Sorting

```python
sorted_list = sorted(my_list)
sorted_dict = sorted(my_dict.items(), key=lambda item: item[1])
```

#### Basic Input/Output

```python
user_input = input("Enter your name: ")
print("Hello,", user_input)
```

### Working with Files

#### Reading Files

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

#### Writing Files

```python
with open("file.txt", "w") as file:
    file.write("Hello, World!")
```

### Networking

#### HTTP Requests

```python
import requests

response = requests.get("http://example.com")
print(response.status_code)
print(response.text)
```

#### Socket Programming

```python
import socket

s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect(("example.com", 80))
s.sendall(b"GET / HTTP/1.1\r\nHost: example.com\r\n\r\n")
response = s.recv(4096)
print(response)
s.close()
```

### Security-Related Modules

#### Hashing

```python
import hashlib

# MD5
hash_md5 = hashlib.md5(b"password").hexdigest()
print(f"MD5: {hash_md5}")

# SHA-256
hash_sha256 = hashlib.sha256(b"password").hexdigest()
print(f"SHA-256: {hash_sha256}")
```

#### Encryption and Decryption

**Using `cryptography` Library**

```python
from cryptography.fernet import Fernet

# Generate a key
key = Fernet.generate_key()
cipher_suite = Fernet(key)

# Encrypt a message
cipher_text = cipher_suite.encrypt(b"Secret message")
print(f"Encrypted: {cipher_text}")

# Decrypt the message
plain_text = cipher_suite.decrypt(cipher_text)
print(f"Decrypted: {plain_text}")
```

#### Password Hashing

```python
from passlib.hash import pbkdf2_sha256

# Hash a password
hashed = pbkdf2_sha256.hash("password")
print(f"Hashed: {hashed}")

# Verify a password
is_correct = pbkdf2_sha256.verify("password", hashed)
print(f"Password correct: {is_correct}")
```

### Web Scraping

#### Using `BeautifulSoup`

```python
from bs4 import BeautifulSoup
import requests

response = requests.get("http://example.com")
soup = BeautifulSoup(response.text, 'html.parser')

for link in soup.find_all('a'):
    print(link.get('href'))
```

### Working with JSON

```python
import json

# Parse JSON
data = '{"name": "Alice", "age": 25}'
parsed_data = json.loads(data)
print(parsed_data)

# Convert to JSON
dict_data = {"name": "Bob", "age": 30}
json_data = json.dumps(dict_data)
print(json_data)
```

### Command Execution

#### Using `subprocess` Module

```python
import subprocess

# Run a command and get the output
result = subprocess.run(["ls", "-la"], capture_output=True, text=True)
print(result.stdout)
```

### Regular Expressions

```python
import re

pattern = r"\b[A-Za-z]+\b"
text = "The quick brown fox jumps over the lazy dog"

matches = re.findall(pattern, text)
print(matches)
```

### Logging

```python
import logging

logging.basicConfig(level=logging.INFO)
logging.info("This is an info message")
logging.warning("This is a warning message")
logging.error("This is an error message")
```

### Useful Tips

#### Virtual Environments

```sh
# Create a virtual environment
python -m venv venv

# Activate the virtual environment
# On Windows
venv\Scripts\activate
# On Unix or MacOS
source venv/bin/activate

# Install dependencies
pip install -r requirements.txt

# Deactivate the virtual environment
deactivate
```

#### Exception Handling

```python
try:
    result = 10 / 0
except ZeroDivisionError as e:
    print(f"Error: {e}")
finally:
    print("This block is always executed")
```

#### List Comprehensions

```python
squares = [x ** 2 for x in range(10)]
print(squares)
```

#### Dictionary Comprehensions

```python
squares_dict = {x: x ** 2 for x in range(10)}
print(squares_dict)
```

#### Using `itertools` for Efficient Iteration

```python
import itertools

permutations = list(itertools.permutations([1, 2, 3]))
print(permutations)

combinations = list(itertools.combinations([1, 2, 3], 2))
print(combinations)
```

#### Using `collections` for Advanced Data Structures

```python
from collections import Counter, defaultdict, deque

# Counter
counter = Counter("hello world")
print(counter)

# Defaultdict
default_dict = defaultdict(int)
default_dict["key"] += 1
print(default_dict)

# Deque
deque_list = deque([1, 2, 3])
deque_list.appendleft(0)
print(deque_list)
```

#### Using `os` for System Operations

```python
import os

# Get current working directory
cwd = os.getcwd()
print(cwd)

# List files in directory
files = os.listdir(".")
print(files)

# Execute a system command
os.system("echo Hello, World!")
```

### Penetration Testing Tools

#### `scapy` for Network Packet Manipulation

```python
from scapy.all import *

# Create a packet
packet = IP(dst="192.168.1.1")/ICMP()
# Send the packet
send(packet)
```

#### `nmap` for Network Scanning

```python
import nmap

nm = nmap.PortScanner()
nm.scan('127.0.0.1', '22-443')
print(nm.csv())
```

#### `socket` for Simple Network Connections

```python
pythonCopy codeimport socket

# Create a socket object
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
# Connect to a server
s.connect(('localhost', 8080))
# Send data
s.sendall(b'Hello, World!')
# Receive data
data = s.recv(1024)
print('Received', repr(data))
# Close the connection
s.close()
```