>>> n = 100
>>> s = "We have " + str(n) + " apples."
>>> s
'We have 100 apples.'

>>> s = "abc"
>>> t = "abc"
>>> k = "abd"
>>> s == t
True
>>> t != k
True
>>> s == k
False

>>> len("abcdef")
6

>>> s = "Python"
>>> s[0]
'P'
>>> s[len(s)-1]
'n'

>>> s = "Python"
>>> s[100]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
IndexError: string index out of range

>>> s = "Python"
>>> s[-1]
'n'
>>> s[-len(s)]
'P'

[a:b]   # 从索引a（包含）到索引b（不包含）的字符组成的子串

>>> s = "Python"
>>> s[1:3]      # 包含索引1的字符但不包含索引3的字符
'yt'

>>> s = "Python"
>>> s[:3]
'Pyt'
>>> s[1:]
'ython'

>>> s = "Python"
>>> s[-3:]          # 从倒数第三个字符开始到最后一个字符
'hon'

>>> s = "Python"
>>> s[0] = 'p'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'str' object does not support item assignment

>>> s = "Python"
>>> s = 'p' + s[1:]
>>> s
'python'

>>> n = 10
>>> sum = 100
>>> f"the value of n is {n}, the value of sum is {sum}"
'the value of n is 10, the value of sum is 100'

>>> n = 10
>>> sum = 100
>>> "the value of n is {n}, the value of sum is {sum}"
'the value of n is {n}, the value of sum is {sum}'

>>> l = list()      # 创建空列表
>>> l = []          # 创建空列表
>>> l = [1,2,3,4]   # 创建带4个数字的列表

>>> l = [1,2,3,4]
>>> l[2]
3
>>> l[1:3]
[2, 3]

>>> l = [1,2,3,4]
>>> l += [5,6]
>>> l
[1, 2, 3, 4, 5, 6]

>>> l = [0,2,3,4]
>>> l[0]=1      # 修改0号元素的值
>>> l
[1, 2, 3, 4]

>>> l1 = [1,2,3,4]
>>> l2 = l1           # l2其实是l1的一个引用
>>> l1[0] = 233       # 修改l1的0号元素
>>> l2                # 发现l2也发生了改变
[233, 2, 3, 4]

>>> l = [1,2,3,4]
>>> len(l)
4

>>> l = [[1,2,3,4], ['a','b','c'], 12.34]
>>> l[0][1]
2
>>> l[1][2]
'c'
>>> l[2]
12.34

>>> l = [1,2,3,4]
>>> 1 in l
True
>>> 5 in l
False

>>> print("Hello!")
Hello!
>>> print("Hello!\n")   # 多输出一个换行
Hello!

>>> print(23.4)
23.4
>>> print([1,2,3,4])    # 打印列表
[1, 2, 3, 4]

>>> print("Hello", end="123")
Hello123>>> # 会发现没有换行了

>>> x = input() # 下面一行是键盘的输入
123
>>> x           # x是字符串
'123'
>>> y = int(x)
>>> print(y*2)
246

>>> x = input()
123 456 7 8 9
>>> x
'123 456 7 8 9'

n = input("Please enter n:")

# 相当于：
print("Please enter n:", end='')
n = input()

for i in range(100):
    if i % 2 == 0:                  # 4个空格，代表属于for循环下的语句
        print(str(i) + " is even")  # 8个空格，属于if语句
    else:                           # 4个空格，属于for语句
        print(str(i) + " is odd")   # 8个空格，属于else语句

if condition1:
    # 满足条件1
    pass
elif condition2:
    # 不满足条件1，满足条件2
    pass
elif condition3:
    # 不满足条件1、2，满足条件3
    pass
else:
    # 不满足条件1、2、3
    pass

# 从用户输入成绩
score = int(input("Please enter your score: "))

# 判断成绩等级
if score >= 90:
    print("Grade: A")
elif score >= 80:
    print("Grade: B")
elif score >= 70:
    print("Grade: C")
elif score >= 60:
    print("Grade: D")
else:
    print("Grade: F")

# 提示用户输入年龄
age = int(input("Enter your age: "))

# 提示用户是否有学生证
has_student_id = int(input("Do you have a student ID? (1 for Yes, 0 for No): "))

# 提示用户是否为老年人
is_senior = int(input("Are you a senior citizen? (1 for Yes, 0 for No): "))

# 检查年龄是否合法
if age > 0:        
    if is_senior:
        print("You are eligible for a senior discount.")
    elif has_student_id:
        print("You are eligible for a student discount.")
    else:
        if age < 18:
            print("You are eligible for a child discount.")
        elif age <= 64:
            print("You are eligible for a standard adult ticket.")
        else:
            print("You are eligible for a senior discount.")
else:
    print("Invalid age entered.")

while cond:
    # 循环执行直到cond为假值
    pass

# 初始化总和和当前数字
sum = 0
number = 1
n = int(input("Enter a positive integer: "))
while number <= n:
    sum += number
    number += 1
print(f"The sum of numbers from 1 to {n} is: {sum}")

for 元素 in 可迭代序列:
    pass

lang = ["CPP", "Python", "Java", "Assembly", "C"]
for s in lang:
    print(f"{s} {len(s)}")

CPP 3
Python 6
Java 4
Assembly 8
C 1

s = "Hello World!"
i = 0
for c in s:
    print(f"index of {i} is: {c}")
    i += 1

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

print("range(5)")
for i in range(5):
    print(i)
print("range(2,5)")
for i in range(2, 5):
    print(i)
print("range(2,10,2)")
for i in range(2, 10, 2):
    print(i)

# 预设的数字
secret_number = 42
guess = None
print("Guess the number (between 1 and 100):")
# 无限循环，直到猜对数字
while True:
    guess = int(input())
    if guess < secret_number:
        print("Too low! Try again:")
    elif guess > secret_number:
        print("Too high! Try again:")
    else:
        print("Congratulations! You've guessed the right number.")
        break  # 猜对了，退出循环

numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
print("Even numbers in the list:")
for number in numbers:
    if number % 2 != 0:
        continue
    print(number)

while cond:
    pass
else:
    # 只有while循环结束时未执行break才会执行这部分
    pass

for n in range(2, 10):
    for x in range(2, n):
        if n % x == 0:
            print(f'{n} is not a prime number')
            # 执行break，不执行for语句的else
            break
    else:   # 注意这个else属于第二个for，而不是if的
        # range(2,n)都不能整除n，说明n没有因子
        print(f'{n} is a prime number')

# 不可变对象
a = 10
b = a  # b 也引用整数 10
print(id(a), id(b))  # 两者的 id 相同

a += 1  # a 的值改变
print(a)  # 输出 11
print(b)  # 仍然输出 10，因为 b 仍然引用原来的对象

def swap(a, b):
    tmp = a
    a = b
    b = tmp

a = 2
b = 3
swap(a, b)
print(a, b)     # a和b仍然为2和3，因为a仍然指向2的引用，b仍然指向3的引用

# 可变对象
list1 = [1, 2, 3]
list2 = list1  # list2 也引用 list1
list2.append(4)  # 修改 list2
print(list1)  # 输出 [1, 2, 3, 4]，list1 也被改变

def add(l, x):
    l.append(x)

l = [1, 2, 3]
print(l)        # 输出[1, 2, 3]
add(l, 4)
print(l)        # 输出[1, 2, 3, 4]，函数可以改变外部传递过来的列表！

def 函数名(形参列表):
    # 语句
    pass

def Fibo(n):
    """
    返回第n项的Fibonacci数列值，n应该为大于0的整数
    返回值为整数
    """
    if n<1:
        return      # n不符合要求直接退出函数，此时函数的返回值为None
    if n==1 or n==2:
        return 1
    return Fibo(n-1) + Fibo(n-2)

def fun(a):
    if type(a) != int:
        return
    if a == 1:
        return True
    if a == 2:
        return "Hello"
    return a

def f1(a, b, c):
    # 定义了3个形参的函数
    pass
def f2(a, b):
    # 定义了2个形参的函数
    pass

def ask_ok(prompt, retries=4, reminder='Please try again!'):
    while True:
        reply = input(prompt)
        if reply in {'y', 'ye', 'yes'}:
            return True
        if reply in {'n', 'no', 'nop', 'nope'}:
            return False
        retries = retries - 1
        if retries < 0:
            raise ValueError('invalid user response')
        print(reminder)

i = 5
def f(arg=i):
    print(arg)

if __name__ == "__main__":
    i = 6
    f()

def f(a, L=[]):
    L.append(a)
    return L
print(f(1))
print(f(2))
print(f(3))

def f(a, L=None):
    if L is None:
        L = []
    L.append(a)
    return L

def parrot(voltage, state='a stiff', action='voom', type='Norwegian Blue'):
    print("-- This parrot wouldn't", action, end=' ')
    print("if you put", voltage, "volts through it.")
    print("-- Lovely plumage, the", type)
    print("-- It's", state, "!")

parrot(1000)                                          # 1 个位置参数
parrot(voltage=1000)                                  # 1 个关键字参数
parrot(voltage=1000000, action='VOOOOOM')             # 2 个关键字参数
parrot(action='VOOOOOM', voltage=1000000)             # 2 个关键字参数
parrot('a million', 'bereft of life', 'jump')         # 3 个位置参数
parrot('a thousand', state='pushing up the daisies')  # 1 个位置参数，1 个关键字参数

parrot()                     # 缺失必需的参数
parrot(voltage=5.0, 'dead')  # 关键字参数后存在非关键字参数
parrot(110, voltage=220)     # 同一个参数重复的值
parrot(actor='John Cleese')  # 未知的关键字参数

import os

print(os.getcwd())          # 输出当前的运行目录
print(os.listdir('.'))      # 列出当前目录下的所有文件和子目录

import math

# 计算 C(5, 2)
print(math.comb(5, 2))  # 输出 10
print(math.sqrt(16))  # 输出 4.0
# 计算正弦和余弦
angle = math.pi / 4  # 45 degrees
print(math.sin(angle))  # 输出 0.7071...
print(math.cos(angle))  # 输出 0.7071...

import random
print(random.randint(1, 100))  # 输出 1 到 100 之间的随机整数

import datetime
now = datetime.datetime.now()
print(now)  # 输出当前日期和时间

from math import comb, sqrt, sin, cos, pi

# 计算 C(5, 2)
print(comb(5, 2))  # 输出 10
print(sqrt(16))  # 输出 4.0
# 计算正弦和余弦
angle = pi / 4  # 45 degrees
print(sin(angle))  # 输出 0.7071...
print(cos(angle))  # 输出 0.7071...

from random import randint
print(randint(1, 100))  # 输出 1 到 100 之间的随机整数

from datetime import datetime
now = datetime.now()
print(now)  # 输出当前日期和时间

from random import randint as rdi
print(rdi(1, 100))      # rdi 为randint的别名

import datetime as dt
print(dt.datetime.now())    # dt为datetime模块的别名

list.append(x)
# 在列表末尾添加一个元素。

list.extend(otherList)
# 将其他列表的元素添加到list列表的尾部。

list.insert(i, x)
# 在指定位置插入元素。第一个参数是插入元素的索引。
# 因此，a.insert(0, x) 在列表开头插入元素， a.insert(len(a), x) 等同于 a.append(x) 。

list.remove(x)
# 从列表中删除第一个值为 x 的元素。未找到指定元素时，触发ValueError异常。

list.clear()
# 删除列表里的所有元素。

list.index(x[, start[, end]])
# 返回列表中第一个值为 x 的元素的零基索引。未找到指定元素时，触发ValueError异常。
# 可选参数start和end是切片符号，相当于搜索子序列。
# 返回的索引是相对于整个序列的开始计算的，而不是 start 参数。

list.count(x)
# 返回列表中元素x出现的次数。

list.sort(*, key=None, reverse=False)
# 排序列表中的元素。key为比较函数，注意这两个形参必须以关键字参数的形式给出

list.reverse()
# 翻转列表中的元素。

list.copy()
# 返回列表的浅拷贝。相当于 a[:] 。

>>> fruits = ['orange', 'apple', 'pear', 'banana', 'kiwi', 'apple', 'banana']
>>> fruits.count('apple')
2
>>> fruits.count('tangerine')
0
>>> fruits.index('banana')
3
>>> fruits.index('banana', 4)  # 从 4 号位开始查找下一个 banana
6
>>> fruits.reverse()
>>> fruits
['banana', 'apple', 'kiwi', 'banana', 'pear', 'apple', 'orange']
>>> fruits.append('grape')
>>> fruits
['banana', 'apple', 'kiwi', 'banana', 'pear', 'apple', 'orange', 'grape']
>>> fruits.sort()
>>> fruits
['apple', 'apple', 'banana', 'banana', 'grape', 'kiwi', 'orange', 'pear']

>>> squares = []
>>> for x in range(10):
...     squares.append(x**2)
... 
>>> squares
[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

>>> squares = [x**2 for x in range(10)]
>>> squares
[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

>>> [(x, y) for x in [1,2,3] for y in [3,1,4] if x != y]
[(1, 3), (1, 4), (2, 3), (2, 1), (2, 4), (3, 1), (3, 4)]

>>> combs = []
>>> for x in [1,2,3]:
...     for y in [3,1,4]:
...         if x != y:
...             combs.append((x, y))
... 
>>> combs
[(1, 3), (1, 4), (2, 3), (2, 1), (2, 4), (3, 1), (3, 4)]

>>> t = (12345, 54321, 'hello!')
>>> t[0]
12345
>>> t
(12345, 54321, 'hello!')
>>> # 元组可以嵌套：
>>> u = t, (1, 2, 3, 4, 5)
>>> u
((12345, 54321, 'hello!'), (1, 2, 3, 4, 5))
>>> # 元组是不可变对象：
>>> t[0] = 88888
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'tuple' object does not support item assignment

>>> t = (12345, 54321, 'hello!')
>>> x, y, z = t     # 将t的三个元素分别传给x y z
>>> x
12345
>>> y
54321
>>> z
'hello!'

>>> basket = {'apple', 'orange', 'apple', 'pear', 'orange', 'banana'}
>>> print(basket)                      # 显示重复项已被移除
{'orange', 'banana', 'pear', 'apple'}

>>> 'orange' in basket                 # 快速成员检测
True
>>> 'crabgrass' in basket
False

>>> # 演示针对两个单词中独有的字母进行集合运算
>>> a = set('abracadabra')
>>> b = set('alacazam')
>>> a                                  # a 中独有的字母
{'a', 'r', 'b', 'c', 'd'}
>>> b
{'c', 'l', 'm', 'a', 'z'}

>>> a - b                              # 存在于 a 中但不存在于 b 中的字母
{'r', 'd', 'b'}
>>> a | b                              # 存在于 a 或 b 中或两者中皆有的字母
{'a', 'c', 'r', 'd', 'b', 'm', 'z', 'l'}
>>> a & b                              # 同时存在于 a 和 b 中的字母
{'a', 'c'}
>>> a ^ b                              # 存在于 a 或 b 中但非两者中皆有的字母
{'r', 'd', 'b', 'm', 'z', 'l'}

>>> tel = {'jack': 4098, 'sape': 4139}  # 使用 键:值 的形式初始化字典
>>> tel['guido'] = 4127   # 给不存在的键赋值，相当于插入一个新键
>>> tel
{'jack': 4098, 'sape': 4139, 'guido': 4127}
>>> tel['jack']           # 通过键获取值
4098

>>> tel = {'jack': 4098, 'sape': 4139}
>>> tel['guido'] = 4127
>>> del tel['sape']
>>> tel['irv'] = 4127
>>> tel
{'jack': 4098, 'guido': 4127, 'irv': 4127}

>>> tel = {'jack': 4098, 'sape': 4139}
>>> list(tel)       # 返回的是键的列表
['jack', 'sape']
>>> 'guido' in tel  # 判断键是否存在
False
>>> 'jack' in tel
True
>>> 4098 in tel     # 值不是键
False

>>> dict([('sape', 4139), ('guido', 4127), ('jack', 4098)])
{'sape': 4139, 'guido': 4127, 'jack': 4098}

>>> knights = {'gallahad': 'the pure', 'robin': 'the brave'}
>>> for k, v in knights.items():
...     print(k, v)
... 
gallahad the pure
robin the brave

>>> tel = {'jack': 4098, 'guido': 4127, 'irv': 4127}
>>> list(tel.values())
[4098, 4127, 4127]
>>> list(tel.keys())
['jack', 'guido', 'irv']
>>> list(tel)
['jack', 'guido', 'irv']

class ClassName:
    <语句-1>
    .
    .
    .
    <语句-N>

class MyClass:
    """一个简单的示例类"""
    i = 12345                   # 类变量

    @staticmethod           # 静态方法，下面讲
    def f():                # 类的方法
        return 'hello world'
    def f2(self):                # 类的方法，为什么要写self将在下面讲
        return 'hello world'

class MyClass:
    """一个简单的示例类"""
    i = 12345                   # 类变量

    @staticmethod
    def f():                # 类的方法
        return 'hello world'
    def f2(self):                # 类的方法
        return 'hello world'
x = MyClass()

def __init__(self):
    self.data = []

class Person:
    def __init__(self, name):
        self.name = name
        print(f"Hello, {name}!")

a = Person("Kotori")

class Person:
    def __init__(self, name):
        self.name = name
        print(f"Hello, {name}!")
    def getName(self):
        return self.name

a = Person("Alice")
b = Person("Bob")
print(a.name)
print(b.name)
print(a.getName())
print(b.getName())

class Dog:
    kind = 'canine'         # 类变量被所有实例所共享
    def __init__(self, name):
        self.name = name    # 实例变量为每个实例所独有
>>> d = Dog('Fido')
>>> e = Dog('Buddy')
>>> d.kind                  # 被所有的 Dog 实例所共享
'canine'
>>> e.kind                  # 被所有的 Dog 实例所共享
'canine'
>>> d.name                  # 为 d 所独有
'Fido'
>>> e.name                  # 为 e 所独有
'Buddy'

class 子类(父类):
    pass
class DerivedClassName(BaseClassName):
    <语句-1>
    .
    .
    .
    <语句-N>

class Derived(Base):
    def __init__(self):
        super().__init__()      # 如果有其他形参需要给出

class Parent:
    def __init__(self):
        self.parent_attribute = "I am a parent"

    def parent_method(self):
        print("This is a method from the parent class.")

class Child(Parent):  # Child 继承 Parent
    def __init__(self):
        super().__init__()  # 调用父类的构造函数
        self.child_attribute = "I am a child"

    def child_method(self):
        print("This is a method from the child class.")

    def parent_method(self):  # 重写父类的方法
        print("This is an overridden method from the child class.")

# 使用示例
child_instance = Child()
print(child_instance.parent_attribute)  # 输出: I am a parent
print(child_instance.child_attribute)    # 输出: I am a child
child_instance.parent_method()           # 输出: This is an overridden method from the child class.

# 函数最常用的形参，其中encodeing为关键字参数
open(filename, mode='r', encoding=None)