Functions là gì?
Functions là các khối code có thể tái sử dụng, giúp tổ chức và modularize chương trình.
Định nghĩa Function
# Cú pháp cơ bản
def greet():
print("Hello, World!")
# Gọi function
greet() # Hello, World!
# Function với docstring
def scan_port():
"""
Scan a single port.
Returns True if port is open.
"""
passParameters và Arguments
# Positional parameters
def greet(name):
print(f"Hello, {name}!")
greet("Alice") # Hello, Alice!
# Multiple parameters
def scan_port(host, port):
print(f"Scanning {host}:{port}")
scan_port("192.168.1.1", 80)
# Default parameters
def scan_port(host, port=80, timeout=1.0):
print(f"Scanning {host}:{port} (timeout: {timeout}s)")
scan_port("192.168.1.1") # port=80, timeout=1.0
scan_port("192.168.1.1", 443) # port=443, timeout=1.0
scan_port("192.168.1.1", timeout=2.0) # Keyword argumentReturn Values
# Single return value
def add(a, b):
return a + b
result = add(5, 3) # 8
# Multiple return values (tuple)
def get_server_info():
return "192.168.1.1", 443, "HTTPS"
ip, port, protocol = get_server_info()
# Early return
def is_valid_port(port):
if port < 1 or port > 65535:
return False
return True*args và **kwargs
# *args - variable positional arguments
def scan_ports(host, *ports):
for port in ports:
print(f"Scanning {host}:{port}")
scan_ports("192.168.1.1", 22, 80, 443, 3306)
# **kwargs - variable keyword arguments
def create_request(url, **options):
print(f"URL: {url}")
for key, value in options.items():
print(f" {key}: {value}")
create_request(
"https://api.example.com",
method="POST",
timeout=30,
headers={"Auth": "Bearer token"}
)
# Kết hợp
def api_call(endpoint, *args, **kwargs):
print(f"Endpoint: {endpoint}")
print(f"Args: {args}")
print(f"Kwargs: {kwargs}")Type Hints
from typing import List, Dict, Optional, Tuple
def scan_port(host: str, port: int, timeout: float = 1.0) -> bool:
"""
Scan a single port on host.
Args:
host: Target hostname or IP
port: Port number to scan
timeout: Connection timeout in seconds
Returns:
True if port is open, False otherwise
"""
# Implementation
return True
def get_open_ports(host: str, ports: List[int]) -> List[int]:
"""Return list of open ports."""
open_ports = []
for port in ports:
if scan_port(host, port):
open_ports.append(port)
return open_ports
def find_service(port: int) -> Optional[str]:
"""Return service name or None if not found."""
services = {22: "SSH", 80: "HTTP", 443: "HTTPS"}
return services.get(port)Lambda Functions
# Anonymous functions
square = lambda x: x ** 2
print(square(5)) # 25
# Với sorted()
servers = [
{"name": "web1", "load": 85},
{"name": "web2", "load": 45},
{"name": "web3", "load": 70}
]
# Sắp xếp theo load
sorted_servers = sorted(servers, key=lambda s: s["load"])
# Với filter()
ports = [22, 80, 443, 8080, 3306]
secure_ports = list(filter(lambda p: p in [443, 22], ports))
# [22, 443]
# Với map()
doubled = list(map(lambda x: x * 2, [1, 2, 3]))
# [2, 4, 6]Scope và Closures
# Global vs Local scope
global_var = "I'm global"
def outer():
outer_var = "I'm outer"
def inner():
inner_var = "I'm inner"
print(global_var) # Accessible
print(outer_var) # Accessible
print(inner_var) # Accessible
inner()
# Closure - function nhớ scope của nó
def create_scanner(host):
def scan(port):
print(f"Scanning {host}:{port}")
return scan
scanner = create_scanner("192.168.1.1")
scanner(80) # Scanning 192.168.1.1:80
scanner(443) # Scanning 192.168.1.1:443Decorators
import time
from functools import wraps
# Basic decorator
def timer(func):
@wraps(func)
def wrapper(*args, **kwargs):
start = time.time()
result = func(*args, **kwargs)
end = time.time()
print(f"{func.__name__} took {end - start:.2f}s")
return result
return wrapper
@timer
def slow_function():
time.sleep(1)
return "Done"
slow_function() # slow_function took 1.00s
# Decorator with arguments
def retry(times=3):
def decorator(func):
@wraps(func)
def wrapper(*args, **kwargs):
for attempt in range(times):
try:
return func(*args, **kwargs)
except Exception as e:
print(f"Attempt {attempt + 1} failed: {e}")
raise Exception(f"Failed after {times} attempts")
return wrapper
return decorator
@retry(times=3)
def flaky_request():
# Might fail sometimes
passỨng dụng: Port Scanner Function
import socket
from typing import List, Tuple
from concurrent.futures import ThreadPoolExecutor
def scan_single_port(host: str, port: int, timeout: float = 1.0) -> Tuple[int, bool]:
"""Scan a single port."""
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
sock.settimeout(timeout)
try:
result = sock.connect_ex((host, port))
return (port, result == 0)
finally:
sock.close()
def scan_ports(
host: str,
ports: List[int],
threads: int = 100
) -> List[int]:
"""Scan multiple ports with threading."""
open_ports = []
with ThreadPoolExecutor(max_workers=threads) as executor:
futures = [
executor.submit(scan_single_port, host, port)
for port in ports
]
for future in futures:
port, is_open = future.result()
if is_open:
open_ports.append(port)
return sorted(open_ports)
# Usage
if __name__ == "__main__":
target = "scanme.nmap.org"
ports = list(range(1, 1025))
open_ports = scan_ports(target, ports)
print(f"Open ports: {open_ports}")Bước tiếp theo
Trong bài tiếp theo:
- File I/O: Đọc và ghi files
- Exception Handling: Try/except
- Context Managers: with statement
💡 Pro tip: Một function nên làm một việc duy nhất. Nếu function quá dài, hãy chia nhỏ!