>>> import this
The Zen of Python, by Tim Peters

Beautiful is better than ugly.
Explicit is better than implicit.
Simple is better than complex.
Complex is better than complicated.
Flat is better than nested.
Sparse is better than dense.
Readability counts.

>>> 2 + 3
5
>>> print("Hello, World!")
Hello, World!
>>> x = 42
>>> x
42

# hello.py
print("Hello, World!")
name = input("What is your name? ")
print(f"Hello, {name}!")

$ python hello.py

# 变量不需要声明类型
x = 42        # x 是整数
x = "hello"   # x 现在是字符串（类型变了！）
x = [1, 2, 3] # x 现在是列表

# 同一个变量可以指向不同类型的对象
def demo(x):
    print(type(x), x)

demo(42)       # <class 'int'> 42
demo("hello")  # <class 'str'> hello
demo([1, 2])   # <class 'list'> [1, 2]

# Python 不会隐式转换
"1" + 2  # TypeError: can only concatenate str (not "int") to str

# 需要显式转换
int("1") + 2    # 3
str(1) + "2"    # "12"

# 对比 JavaScript（弱类型）
# "1" + 2 = "12"（JavaScript 会隐式转换）

# 鸭子类型
class Duck:
    def quack(self):
        return "Quack!"

class Person:
    def quack(self):
        return "I'm quacking like a duck!"

def make_it_quack(thing):
    print(thing.quack())

make_it_quack(Duck())    # Quack!
make_it_quack(Person())  # I'm quacking like a duck!
# 不关心类型，只关心是否有 quack 方法

# 整数（任意精度）
x = 42
y = 10 ** 100  # 大整数

# 浮点数
pi = 3.14159
e = 2.71828

# 复数
z = 3 + 4j
print(z.real, z.imag)  # 3.0 4.0

# 布尔值
True, False
bool(0)    # False
bool("")   # False
bool([])   # False
bool(None) # False
bool(1)    # True

# 字符串
s = "Hello, World!"
s = 'Hello, World!'  # 单引号和双引号等价

# 多行字符串
text = """This is
a multi-line
string."""

# 原始字符串（不处理转义）
path = r"C:\Users\Alice\Documents"

# f-string（格式化字符串，Python 3.6+）
name = "Alice"
age = 30
print(f"My name is {name} and I'm {age} years old.")
print(f"Next year I'll be {age + 1}.")

# 字符串操作
"hello".upper()        # "HELLO"
"HELLO".lower()        # "hello"
"hello world".title()  # "Hello World"
"  hello  ".strip()    # "hello"
"hello".replace("l", "L")  # "heLLo"
"hello world".split()  # ["hello", "world"]
", ".join(["a", "b", "c"])  # "a, b, c"
"hello".startswith("he")    # True
"hello".endswith("lo")      # True
"hello".find("ll")          # 2

# 列表（可变序列）
numbers = [1, 2, 3, 4, 5]
mixed = [1, "hello", 3.14, True]

# 访问元素
numbers[0]    # 1
numbers[-1]   # 5（最后一个）
numbers[1:3]  # [2, 3]（切片）

# 修改
numbers[0] = 10       # [10, 2, 3, 4, 5]
numbers.append(6)     # [10, 2, 3, 4, 5, 6]
numbers.insert(0, 0)  # [0, 10, 2, 3, 4, 5, 6]
numbers.pop()         # 6
numbers.remove(10)    # [0, 2, 3, 4, 5]

# 列表操作
len(numbers)          # 5
sorted(numbers)       # [0, 2, 3, 4, 5]
reversed(numbers)     # <list_reverseiterator>
list(reversed(numbers))  # [5, 4, 3, 2, 0]

# 列表推导式
squares = [x**2 for x in range(10)]
evens = [x for x in range(20) if x % 2 == 0]

# 字典（键值对）
person = {"name": "Alice", "age": 30, "city": "NYC"}

# 访问
person["name"]          # "Alice"
person.get("email", "N/A")  # "N/A"（不存在时返回默认值）

# 修改
person["email"] = "alice@example.com"
person.update({"age": 31, "city": "LA"})
del person["email"]

# 遍历
for key in person:
    print(key, person[key])

for key, value in person.items():
    print(key, value)

# 字典推导式
squares = {x: x**2 for x in range(5)}
# {0: 0, 1: 1, 2: 4, 3: 9, 4: 16}

# if/elif/else
x = 42
if x > 0:
    print("positive")
elif x == 0:
    print("zero")
else:
    print("negative")

# for 循环
for i in range(5):
    print(i)

for item in [1, 2, 3]:
    print(item)

for key, value in person.items():
    print(f"{key}: {value}")

# while 循环
count = 0
while count < 5:
    print(count)
    count += 1

# break 和 continue
for i in range(10):
    if i == 3:
        continue  # 跳过 3
    if i == 7:
        break     # 到 7 停止
    print(i)  # 0, 1, 2, 4, 5, 6

# 基本函数
def greet(name):
    return f"Hello, {name}!"

# 默认参数
def power(base, exp=2):
    return base ** exp

power(3)     # 9
power(3, 3)  # 27

# 关键字参数
def create_user(name, age, city="Unknown"):
    return {"name": name, "age": age, "city": city}

create_user("Alice", 30, city="NYC")

# 可变参数
def total(*args):
    return sum(args)

total(1, 2, 3, 4)  # 10

# 关键字可变参数
def config(**kwargs):
    return kwargs

config(host="localhost", port=8080)  # {"host": "localhost", "port": 8080}

# Lambda 表达式
square = lambda x: x ** 2
square(5)  # 25

# 高阶函数
numbers = [1, 2, 3, 4, 5]
list(map(lambda x: x * 2, numbers))      # [2, 4, 6, 8, 10]
list(filter(lambda x: x > 3, numbers))   # [4, 5]

def fizzbuzz(n):
    for i in range(1, n + 1):
        if i % 15 == 0:
            print("FizzBuzz")
        elif i % 3 == 0:
            print("Fizz")
        elif i % 5 == 0:
            print("Buzz")
        else:
            print(i)

fizzbuzz(20)

from collections import Counter

def word_frequency(text):
    words = text.lower().split()
    # 去除标点
    words = [w.strip(".,!?;:\"'()[]{}") for w in words]
    return Counter(words)

text = """
The quick brown fox jumps over the lazy dog.
The dog barked at the fox. The fox ran away.
"""

freq = word_frequency(text)
for word, count in freq.most_common(5):
    print(f"{word}: {count}")