Python Cơ Bản - Phần 2

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

1count = 0
2while count < 5:
3    print(count)
4    count += 1
5
6# break và continue
7while True:
8    user_input = input("Enter 'q' to quit: ")
9    if user_input == 'q':
10        break       # Thoát vòng lặp
11    if user_input == '':
12        continue    # Bỏ qua, lặp tiếp
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 (filter)
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}
16
17# Set comprehension
18unique_lengths = {len(word) for word in ["hello", "world", "hi"]}
19# {2, 5}

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 items
14fruits.remove("banana")      # Remove by value
15fruits.pop()                 # Remove & return last
16fruits.pop(0)                # Remove & return 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
23len(fruits)                  # Length

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 if key missing)
12
13# Modify
14person["age"] = 26                   # Update
15person["job"] = "Data Scientist"     # Add new key
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 (rất hữu ích cho Data Science!)
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 (không thể thay đổi)
14point = (10, 20)
15x, y = point  # Unpacking
16
17# Practical: return multiple values
18def get_min_max(numbers):
19    return min(numbers), max(numbers)  # Returns tuple
20
21lo, hi = get_min_max([3, 1, 4, 1, 5])

1def greet(name):
2    """Chào người dùng - đây là docstring"""
3    return f"Hello, {name}!"
4
5message = greet("MinAI")
6print(message)  # Hello, MinAI!

1# Default parameters
2def greet(name, greeting="Hello"):
3    return f"{greeting}, {name}!"
4
5greet("Alice")           # "Hello, Alice!"
6greet("Alice", "Hi")     # "Hi, Alice!"
7
8# Keyword arguments (gọi theo bất kỳ thứ tự)
9def create_profile(name, age, city):
10    return {"name": name, "age": age, "city": city}
11
12profile = create_profile(age=25, city="Hanoi", name="Bob")
13
14# *args - Nhận số lượng arguments KHÔNG CỐ ĐỊNH
15# Ví dụ: sum_all(1, 2) hoặc sum_all(1, 2, 3, 4, 5) — đều được!
16def sum_all(*args):
17    return sum(args)
18
19sum_all(1, 2, 3, 4, 5)  # 15
20
21# **kwargs - Nhận keyword arguments KHÔNG CỐ ĐỊNH
22# Ví dụ: build_dict(name="Alice", age=25) — gọi với bất kỳ keyword nào
23def build_dict(**kwargs):
24    return kwargs
25
26build_dict(a=1, b=2, c=3)  # {'a': 1, 'b': 2, 'c': 3}
27
28# Kết hợp tất cả
29def func(a, b, *args, **kwargs):
30    print(f"a={a}, b={b}")
31    print(f"args={args}")
32    print(f"kwargs={kwargs}")
33
34func(1, 2, 3, 4, x=10, y=20)
35# a=1, b=2 | args=(3, 4) | kwargs={'x': 10, 'y': 20}

1def get_stats(numbers):
2    """Tính các thống kê cơ bản"""
3    return min(numbers), max(numbers), sum(numbers)/len(numbers)
4
5# Unpacking
6min_val, max_val, avg = get_stats([1, 2, 3, 4, 5])
7print(f"Min: {min_val}, Max: {max_val}, Avg: {avg}")

1# Function thường vs Lambda
2def square(x):
3    return x ** 2
4
5square = lambda x: x ** 2  # Tương đương
6
7# Lambda với nhiều arguments
8add = lambda x, y: x + y

1numbers = [1, 2, 3, 4, 5]
2
3# map - áp dụng function cho từng phần tử
4squares = list(map(lambda x: x**2, numbers))
5# [1, 4, 9, 16, 25]
6
7# filter - lọc phần tử
8evens = list(filter(lambda x: x % 2 == 0, numbers))
9# [2, 4]
10
11# sorted - sắp xếp với key
12students = [
13    {"name": "Alice", "score": 85},
14    {"name": "Bob", "score": 92},
15    {"name": "Charlie", "score": 78}
16]
17sorted_students = sorted(students, key=lambda x: x["score"], reverse=True)
18# Bob (92), Alice (85), Charlie (78)

1numbers = [3, 1, 4, 1, 5, 9, 2, 6]
2
3# Aggregation
4len(numbers)       # 8
5sum(numbers)       # 31
6min(numbers)       # 1
7max(numbers)       # 9
8sorted(numbers)    # [1, 1, 2, 3, 4, 5, 6, 9]
9
10# Logic
11any([False, True, False])   # True  (ít nhất 1 True)
12all([True, True, False])    # False (không phải tất cả)
13
14# Math
15abs(-5)           # 5
16round(3.14159, 2) # 3.14
17pow(2, 10)        # 1024
18
19# reduce - aggregate tuần tự
20from functools import reduce
21total = reduce(lambda x, y: x + y, numbers)  # 31

1def timer(func):
2    """Decorator đo thời gian chạy"""
3    import time
4    def wrapper(*args, **kwargs):
5        start = time.time()
6        result = func(*args, **kwargs)
7        end = time.time()
8        print(f"{func.__name__} took {end-start:.4f} seconds")
9        return result
10    return wrapper
11
12@timer
13def slow_function():
14    import time
15    time.sleep(1)
16    return "Done!"
17
18slow_function()
19# slow_function took 1.0012 seconds

1def repeat(times):
2    """Decorator chạy function nhiều lần"""
3    def decorator(func):
4        def wrapper(*args, **kwargs):
5            for _ in range(times):
6                result = func(*args, **kwargs)
7            return result
8        return wrapper
9    return decorator
10
11@repeat(times=3)
12def say_hello(name):
13    print(f"Hello, {name}!")
14
15say_hello("World")
16# Hello, World! (3 lần)

1from functools import lru_cache
2
3# Caching - Lưu kết quả để không tính lại
4@lru_cache(maxsize=128)
5def fibonacci(n):
6    if n < 2:
7        return n
8    return fibonacci(n-1) + fibonacci(n-2)
9
10print(fibonacci(100))  # Rất nhanh nhờ cache!
11
12# Property decorator
13class Circle:
14    def __init__(self, radius):
15        self._radius = radius
16    
17    @property
18    def area(self):
19        import math
20        return math.pi * self._radius ** 2
21
22circle = Circle(5)
23print(circle.area)  # 78.539...

1# Basic
2try:
3    result = 10 / 0
4except ZeroDivisionError:
5    print("Cannot divide by zero!")
6
7# Multiple exceptions
8try:
9    num = int(input("Enter a number: "))
10    result = 10 / num
11except ValueError:
12    print("Invalid input - not a number!")
13except ZeroDivisionError:
14    print("Cannot divide by zero!")
15
16# Catch all + else + finally
17try:
18    file = open("data.txt", "r")
19    content = file.read()
20except FileNotFoundError:
21    print("File not found!")
22else:
23    print(f"File content: {content}")  # Chạy nếu KHÔNG có lỗi
24finally:
25    print("Cleanup done")  # LUÔN LUÔN chạy

1def validate_age(age):
2    if age < 0:
3        raise ValueError("Age cannot be negative")
4    if age > 150:
5        raise ValueError("Age seems unrealistic")
6    return True
7
8# Custom Exception
9class InvalidDataError(Exception):
10    def __init__(self, message, error_code=None):
11        super().__init__(message)
12        self.error_code = error_code
13
14def process_data(data):
15    if not data:
16        raise InvalidDataError("Data is empty", error_code=1001)
17    return data

1# File handling — tự động đóng file
2with open("data.txt", "r") as file:
3    content = file.read()
4# File tự động đóng khi ra khỏi with block
5
6# Custom context manager
7class Timer:
8    def __enter__(self):
9        import time
10        self.start = time.time()
11        return self
12    
13    def __exit__(self, *args):
14        import time
15        self.end = time.time()
16        print(f"Elapsed: {self.end - self.start:.4f}s")
17
18with Timer():
19    sum([i**2 for i in range(1000000)])

1# Import toàn bộ module
2import math
3print(math.sqrt(16))  # 4.0
4
5# Import với alias (rất phổ biến trong Data Science)
6import pandas as pd
7import numpy as np
8import matplotlib.pyplot as plt
9
10# Import specific functions
11from math import sqrt, pi
12print(sqrt(16))  # 4.0

1# utils.py
2def calculate_mean(numbers):
3    return sum(numbers) / len(numbers)
4
5def calculate_std(numbers):
6    mean = calculate_mean(numbers)
7    variance = sum((x - mean)**2 for x in numbers) / len(numbers)
8    return variance ** 0.5
9
10# main.py
11from utils import calculate_mean, calculate_std
12data = [1, 2, 3, 4, 5]
13print(calculate_mean(data))  # 3.0

1# my_module.py
2def main():
3    print("Running as main script")
4
5if __name__ == "__main__":
6    main()  # Chỉ chạy khi execute trực tiếp, không chạy khi import