Variables trong Python
Variables (biến) là containers để lưu trữ dữ liệu. Python là dynamically typed - không cần khai báo type.
# Khai báo biến - không cần từ khóa
name = "Alice" # string
age = 25 # integer
height = 1.75 # float
is_hacker = True # boolean
# Python tự động xác định type
print(type(name)) # <class 'str'>
print(type(age)) # <class 'int'>
print(type(height)) # <class 'float'>
print(type(is_hacker)) # <class 'bool'>Quy tắc đặt tên
# Hợp lệ
user_name = "admin"
userName = "admin" # camelCase
_private = "secret"
port443 = True
# KHÔNG hợp lệ
# 2fast = "error" # Không bắt đầu bằng số
# user-name = "error" # Không dùng dấu gạch ngang
# class = "error" # Không dùng reserved wordsConvention trong Python (PEP 8)
# Variables và functions: snake_case
user_name = "admin"
max_connections = 100
# Constants: UPPER_SNAKE_CASE
MAX_RETRIES = 3
DEFAULT_PORT = 8080
# Classes: PascalCase
class NetworkScanner:
passData Types cơ bản
Strings (str)
# Khai báo strings
single = 'Hello'
double = "World"
multi_line = """
Đây là multi-line
string với triple quotes
"""
# String operations
name = "Python"
print(len(name)) # 6 - độ dài
print(name.upper()) # PYTHON
print(name.lower()) # python
print(name[0]) # P - first character
print(name[-1]) # n - last character
print(name[0:3]) # Pyt - slicing
# String formatting
version = 3.12
print(f"Python {version}") # f-strings (recommended)
print("Python {}".format(version)) # .format()
print("Python %s" % version) # % formatting (old)Numbers (int, float)
# Integers
port = 443
connections = 1000
hex_value = 0xFF # 255
binary = 0b1010 # 10
# Floats
temperature = 36.6
pi = 3.14159
# Operations
print(10 + 3) # 13 - Addition
print(10 - 3) # 7 - Subtraction
print(10 * 3) # 30 - Multiplication
print(10 / 3) # 3.333... - Division (float)
print(10 // 3) # 3 - Floor division
print(10 % 3) # 1 - Modulo
print(10 ** 3) # 1000 - Power
# Type conversion
float_num = 3.7
int_num = int(float_num) # 3 (truncate)
str_num = str(int_num) # "3"Booleans (bool)
is_active = True
is_admin = False
# Boolean operations
print(True and False) # False
print(True or False) # True
print(not True) # False
# Comparisons return booleans
print(5 > 3) # True
print(5 == 5) # True
print(5 != 3) # True
print(5 >= 5) # True
# Truthy và Falsy
# Falsy: False, None, 0, 0.0, "", [], {}, set()
# Truthy: mọi thứ khác
if "hello": # Truthy
print("Non-empty string is truthy")
if not []: # [] is Falsy
print("Empty list is falsy")Collections
Lists
# List - mutable, ordered collection
ports = [80, 443, 8080, 22]
mixed = [1, "hello", True, 3.14]
# Access elements
print(ports[0]) # 80
print(ports[-1]) # 22
print(ports[1:3]) # [443, 8080]
# Modify
ports.append(3306) # Add to end
ports.insert(0, 21) # Insert at position
ports.remove(80) # Remove by value
ports.pop() # Remove last
ports[0] = 20 # Update by index
# List methods
print(len(ports)) # Length
print(443 in ports) # True - check membership
ports.sort() # Sort in place
sorted_ports = sorted(ports) # Return new sorted list
ports.reverse() # Reverse in place
# List comprehension
squares = [x**2 for x in range(10)]
# [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
even = [x for x in range(20) if x % 2 == 0]
# [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]Dictionaries
# Dictionary - key:value pairs
user = {
"username": "admin",
"password": "secret123",
"port": 22,
"is_active": True
}
# Access
print(user["username"]) # admin
print(user.get("email", "N/A")) # N/A (default if not found)
# Modify
user["email"] = "admin@pion.dev" # Add new key
user["port"] = 443 # Update existing
del user["password"] # Delete key
# Methods
print(user.keys()) # dict_keys(['username', 'port', ...])
print(user.values()) # dict_values(['admin', 443, ...])
print(user.items()) # dict_items([('username', 'admin'), ...])
# Iterate
for key, value in user.items():
print(f"{key}: {value}")
# Dict comprehension
squares = {x: x**2 for x in range(5)}
# {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}Tuples
# Tuple - immutable, ordered
coordinates = (10, 20, 30)
single_element = (42,) # Note the comma!
# Access (same as list)
print(coordinates[0]) # 10
print(coordinates[1:]) # (20, 30)
# Cannot modify!
# coordinates[0] = 5 # TypeError!
# Tuple unpacking
x, y, z = coordinates
print(x, y, z) # 10 20 30
# Common use: multiple return values
def get_server_info():
return ("192.168.1.1", 443, "HTTPS")
ip, port, protocol = get_server_info()Sets
# Set - unique, unordered
ports = {80, 443, 8080, 80} # {80, 443, 8080} - no duplicates
empty_set = set() # Note: {} creates empty dict!
# Operations
ports.add(22)
ports.remove(80)
ports.discard(9999) # No error if not found
# Set operations
set_a = {1, 2, 3, 4}
set_b = {3, 4, 5, 6}
print(set_a | set_b) # Union: {1, 2, 3, 4, 5, 6}
print(set_a & set_b) # Intersection: {3, 4}
print(set_a - set_b) # Difference: {1, 2}
print(set_a ^ set_b) # Symmetric diff: {1, 2, 5, 6}None Type
# None - represents "nothing"
result = None
def find_user(username):
users = {"admin": "Admin User", "guest": "Guest User"}
return users.get(username, None)
user = find_user("hacker")
if user is None:
print("User not found!")Type Hints (Python 3.5+)
# Type hints cho code rõ ràng hơn
def scan_port(host: str, port: int) -> bool:
"""Scan a single port on host"""
# Implementation
return True
# Complex types
from typing import List, Dict, Optional
def get_open_ports(host: str) -> List[int]:
return [80, 443, 22]
def get_user(user_id: int) -> Optional[Dict]:
# Returns dict or None
return {"id": user_id, "name": "admin"}Bài tập thực hành
# Bài tập: Target info dictionary
target = {
"ip": "192.168.1.100",
"hostname": "webserver01",
"ports": [22, 80, 443, 3306],
"os": "Ubuntu 22.04",
"services": {
22: "SSH",
80: "HTTP",
443: "HTTPS",
3306: "MySQL"
}
}
# In thông tin
print(f"Target: {target['hostname']} ({target['ip']})")
print(f"OS: {target['os']}")
print("Open ports:")
for port in target['ports']:
service = target['services'].get(port, "Unknown")
print(f" - {port}: {service}")Bước tiếp theo
Trong bài tiếp theo, chúng ta sẽ học về:
- Control Flow: if/else, loops
- Functions: Định nghĩa và gọi functions
- Error Handling: try/except
💡 Security tip: Không bao giờ hardcode passwords trong code. Sử dụng environment variables hoặc secrets management.