1# Khai báo biến đơn giản
2name = "MinAI"           # String
3age = 25                 # Integer
4price = 19.99            # Float
5is_active = True         # Boolean
6
7# Multiple assignment
8x, y, z = 1, 2, 3
9a = b = c = 0
10
11# Swap values (Pythonic way!)
12x, y = y, x

1# ✅ Hợp lệ
2my_variable = 1
3myVariable = 2      # camelCase
4MyVariable = 3      # PascalCase  
5my_variable_2 = 4
6_private = 5
7
8# ❌ Không hợp lệ
92variable = 1       # Bắt đầu bằng số
10my-variable = 2     # Có dấu gạch ngang
11my variable = 3     # Có khoảng trắng

1# Integer - Số nguyên
2count = 42
3big_num = 1_000_000  # Underscore cho dễ đọc
4
5# Float - Số thực
6pi = 3.14159
7scientific = 1.5e-10  # 1.5 × 10^-10
8
9# String - Chuỗi
10name = "Python"
11message = 'Hello World'
12multiline = """
13This is a
14multiline string
15"""
16
17# Boolean
18is_valid = True
19is_empty = False
20
21# None - Giá trị null
22result = None

1x = 42
2print(type(x))        # <class 'int'>
3print(isinstance(x, int))  # True
4
5# Kiểm tra nhiều kiểu
6print(isinstance(x, (int, float)))  # True

1# String to Number
2num_str = "42"
3num_int = int(num_str)      # 42
4num_float = float(num_str)  # 42.0
5
6# Number to String
7x = 100
8s = str(x)  # "100"
9
10# Boolean conversion
11bool(0)       # False
12bool(1)       # True
13bool("")      # False
14bool("text")  # True
15bool([])      # False
16bool([1,2])   # True

1a, b = 10, 3
2
3print(a + b)   # 13  - Cộng
4print(a - b)   # 7   - Trừ
5print(a * b)   # 30  - Nhân
6print(a / b)   # 3.333... - Chia (float)
7print(a // b)  # 3   - Chia lấy phần nguyên
8print(a % b)   # 1   - Chia lấy dư
9print(a ** b)  # 1000 - Lũy thừa (10^3)

1x, y = 5, 10
2
3print(x == y)  # False - Bằng
4print(x != y)  # True  - Khác
5print(x < y)   # True  - Nhỏ hơn
6print(x <= y)  # True  - Nhỏ hơn hoặc bằng
7print(x > y)   # False - Lớn hơn
8print(x >= y)  # False - Lớn hơn hoặc bằng
9
10# Chained comparison (Pythonic!)
11age = 25
12print(18 <= age < 65)  # True

1a, b = True, False
2
3print(a and b)  # False
4print(a or b)   # True
5print(not a)    # False
6
7# Short-circuit evaluation
8x = 5
9result = x > 0 and x < 10  # True
10
11# Practical example
12name = ""
13display = name or "Anonymous"  # "Anonymous"

1x = 10
2x += 5   # x = x + 5  → 15
3x -= 3   # x = x - 3  → 12
4x *= 2   # x = x * 2  → 24
5x /= 4   # x = x / 4  → 6.0
6x //= 2  # x = x // 2 → 3.0
7x **= 2  # x = x ** 2 → 9.0

1s = "Python Data Science"
2
3# Indexing (0-based)
4print(s[0])      # 'P'
5print(s[-1])     # 'e' (từ cuối)
6
7# Slicing [start:end:step]
8print(s[0:6])    # 'Python'
9print(s[7:])     # 'Data Science'
10print(s[::-1])   # Đảo ngược chuỗi
11
12# Length
13print(len(s))    # 19

1text = "  Hello World  "
2
3# Case methods
4text.lower()      # "  hello world  "
5text.upper()      # "  HELLO WORLD  "
6text.title()      # "  Hello World  "
7text.capitalize() # "  hello world  "
8
9# Whitespace
10text.strip()      # "Hello World"
11text.lstrip()     # "Hello World  "
12text.rstrip()     # "  Hello World"
13
14# Find & Replace
15text.find("World")     # 8 (index)
16text.replace("World", "Python")  # "  Hello Python  "
17
18# Split & Join
19"a,b,c".split(",")     # ['a', 'b', 'c']
20"-".join(['a','b','c']) # "a-b-c"
21
22# Check methods
23"123".isdigit()   # True
24"abc".isalpha()   # True
25"abc123".isalnum() # True

1name = "MinAI"
2price = 19.99
3quantity = 3
4
5# f-string (Python 3.6+) - Khuyến nghị!
6print(f"Hello, {name}!")
7print(f"Total: ${price * quantity:.2f}")
8
9# Format specifiers
10num = 1234.5678
11print(f"{num:.2f}")     # 1234.57 (2 decimals)
12print(f"{num:,.2f}")    # 1,234.57 (with comma)
13print(f"{num:10.2f}")   # '   1234.57' (width 10)
14print(f"{num:>10.2f}")  # '   1234.57' (right align)
15print(f"{num:<10.2f}")  # '1234.57   ' (left align)
16
17# Percentage
18ratio = 0.756
19print(f"{ratio:.1%}")   # 75.6%
20
21# .format() method
22print("Hello, {}!".format(name))
23print("{0} costs ${1:.2f}".format("Item", 9.99))

1score = 85
2
3if score >= 90:
4    grade = "A"
5elif score >= 80:
6    grade = "B"
7elif score >= 70:
8    grade = "C"
9else:
10    grade = "F"
11
12print(f"Grade: {grade}")  # Grade: B
13
14# Ternary operator (one-line if)
15status = "Pass" if score >= 60 else "Fail"

1# Iterate over list
2fruits = ["apple", "banana", "cherry"]
3for fruit in fruits:
4    print(fruit)
5
6# Range
7for i in range(5):       # 0, 1, 2, 3, 4
8    print(i)
9
10for i in range(1, 6):    # 1, 2, 3, 4, 5
11    print(i)
12
13for i in range(0, 10, 2): # 0, 2, 4, 6, 8
14    print(i)
15
16# Enumerate (index + value)
17for idx, fruit in enumerate(fruits):
18    print(f"{idx}: {fruit}")
19
20# Zip (parallel iteration)
21names = ["Alice", "Bob"]
22ages = [25, 30]
23for name, age in zip(names, ages):
24    print(f"{name} is {age}")

1count = 0
2while count < 5:
3    print(count)
4    count += 1
5
6# With break and continue
7while True:
8    user_input = input("Enter 'q' to quit: ")
9    if user_input == 'q':
10        break
11    if user_input == '':
12        continue
13    print(f"You entered: {user_input}")

1# Basic
2squares = [x**2 for x in range(10)]
3# [0, 1, 4, 9, 16, 25, 36, 49, 64, 81]
4
5# With condition
6evens = [x for x in range(20) if x % 2 == 0]
7# [0, 2, 4, 6, 8, 10, 12, 14, 16, 18]
8
9# Nested
10matrix = [[i*j for j in range(3)] for i in range(3)]
11# [[0,0,0], [0,1,2], [0,2,4]]
12
13# Dict comprehension
14squares_dict = {x: x**2 for x in range(5)}
15# {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}

1# Create
2fruits = ["apple", "banana", "cherry"]
3numbers = list(range(1, 6))
4
5# Access
6fruits[0]      # "apple"
7fruits[-1]     # "cherry"
8fruits[1:3]    # ["banana", "cherry"]
9
10# Modify
11fruits.append("orange")      # Add to end
12fruits.insert(1, "grape")    # Insert at index
13fruits.extend(["kiwi"])      # Add multiple
14fruits.remove("banana")      # Remove by value
15fruits.pop()                 # Remove last
16fruits.pop(0)                # Remove by index
17
18# Other methods
19fruits.sort()                # Sort in place
20fruits.reverse()             # Reverse in place
21fruits.index("apple")        # Find index
22fruits.count("apple")        # Count occurrences

1# Create
2person = {
3    "name": "Alice",
4    "age": 25,
5    "city": "Hanoi"
6}
7
8# Access
9person["name"]           # "Alice"
10person.get("name")       # "Alice"
11person.get("job", "N/A") # "N/A" (default)
12
13# Modify
14person["age"] = 26       # Update
15person["job"] = "Data Scientist"  # Add new
16
17# Methods
18person.keys()    # dict_keys(['name', 'age', 'city', 'job'])
19person.values()  # dict_values(['Alice', 26, 'Hanoi', 'Data Scientist'])
20person.items()   # dict_items([('name', 'Alice'), ...])
21
22# Iterate
23for key, value in person.items():
24    print(f"{key}: {value}")

1# Set - Unique values, unordered
2colors = {"red", "green", "blue"}
3colors.add("yellow")
4colors.remove("red")
5
6# Set operations
7a = {1, 2, 3}
8b = {2, 3, 4}
9print(a | b)  # Union: {1, 2, 3, 4}
10print(a & b)  # Intersection: {2, 3}
11print(a - b)  # Difference: {1}
12
13# Tuple - Immutable list
14point = (10, 20)
15x, y = point  # Unpacking