# 单行注释

'''
多行注释
也可以这样写
'''

# 这行不会执行
print("hello")  # 这部分也不会执行

if True:
    print("进入 if")
    print("这一行也属于 if")
print("这一行不属于 if")

if True:
print("hello")   # 错误：没有缩进

print("hello")
print(1, 2, 3)

print(1, 2, 3, sep="-")
print("hello", end=" ")
print("world")

name = input("请输入姓名：")
print(name)

x = input("请输入数字：")
print(type(x))

<class 'str'>

a = int(input("请输入整数："))
b = float(input("请输入小数："))

x = 10
print(type(x))

<class 'int'>

int("123")       # 123
float("3.14")    # 3.14
str(100)         # "100"
list("abc")      # ['a', 'b', 'c']

int("3.14")      # 错，因为 "3.14" 不是整数形式
int(3.14)        # 3，小数部分直接丢掉，不是四舍五入

print(5 / 2)   # 2.5
print(5 // 2)  # 2
print(5 % 2)   # 1

x = 5      # 赋值
x == 5     # 判断 x 是否等于 5

age = 20
print(age >= 18 and age <= 60)  # True

if 18 <= age <= 60:
    print("合法年龄")

print('a' in 'abc')       # True
print(4 in [1, 2, 3])     # False
print('x' not in 'abc')   # True

a is b

a == b

score = 85

if score >= 90:
    print("优秀")
elif score >= 60:
    print("及格")
else:
    print("不及格")

n = int(input("请输入一个整数："))

if n % 2 == 0:
    print("偶数")
else:
    print("奇数")

score = int(input("请输入成绩："))

if score >= 90:
    print("A")
elif score >= 80:
    print("B")
elif score >= 70:
    print("C")
elif score >= 60:
    print("D")
else:
    print("E")

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

range(stop)
range(start, stop)
range(start, stop, step)

list(range(5))          # [0, 1, 2, 3, 4]
list(range(1, 5))       # [1, 2, 3, 4]
list(range(1, 10, 2))   # [1, 3, 5, 7, 9]
list(range(10, 1, -2))  # [10, 8, 6, 4, 2]

i = 1
while i <= 5:
    print(i)
    i += 1

for i in range(1, 6):
    if i == 3:
        break
    print(i)

for i in range(1, 6):
    if i == 3:
        continue
    print(i)

n = int(input("请输入 n："))
s = 0

for i in range(1, n + 1):
    s += i

print(s)

n = int(input("请输入 n："))
s = 0

for i in range(1, n + 1):
    if i % 2 == 0:
        s += i

print(s)

s1 = 'hello'
s2 = "hello"
s3 = '''hello'''

s = "python"
print(s[0])   # p
print(s[1])   # y
print(s[-1])  # n
print(s[-2])  # o

字符串[开始:结束:步长]

s = "python"

print(s[0:2])    # py
print(s[1:4])    # yth
print(s[:3])     # pyt
print(s[3:])     # hon
print(s[::-1])   # nohtyp，字符串反转

s = "abc"
s[0] = "x"   # 错误

s = "abc"
s = "x" + s[1:]
print(s)  # xbc

nums = [1, 2, 3, 4]
names = ["Tom", "Jerry"]
mix = [1, "a", 3.14]

lst = [10, 20, 30, 40]

print(lst[0])     # 10
print(lst[-1])    # 40
print(lst[1:3])   # [20, 30]

lst = [1, 2, 3]
lst.append(4)       # 末尾加 4
lst.insert(1, 99)   # 在下标 1 的位置插入 99
print(lst)

lst = [1, 2, 3, 2]

lst.remove(2)   # 删除第一个 2
x = lst.pop()   # 删除并返回最后一个元素
lst.clear()     # 清空列表

lst = [1, 2, 3]
lst[0] = 100
print(lst)  # [100, 2, 3]

lst = [10, 20, 30]
print(20 in lst)       # True
print(lst.index(20))   # 1

lst = [3, 1, 4, 2]
lst.sort()
print(lst)   # [1, 2, 3, 4]

lst.sort(reverse=True)
print(lst)   # [4, 3, 2, 1]

lst = [3, 1, 4, 2]
new_lst = sorted(lst)
print(lst)      # [3, 1, 4, 2]
print(new_lst)  # [1, 2, 3, 4]

lst = [10, 20, 30]

for x in lst:
    print(x)

lst = [10, 20, 30]

for i in range(len(lst)):
    print(i, lst[i])

for i, x in enumerate(lst):
    print(i, x)

lst = []
for i in range(1, 6):
    lst.append(i * i)

lst = [i * i for i in range(1, 6)]
print(lst)  # [1, 4, 9, 16, 25]

lst = [i for i in range(1, 11) if i % 2 == 0]
print(lst)  # [2, 4, 6, 8, 10]

t = (1, 2, 3)
print(t[0])

t[0] = 100   # 错误，元组不可变

t = (1,)

t = (1)
print(type(t))  # int，不是 tuple

student = {
    "name": "Tom",
    "age": 18,
    "score": 90
}

student = {"name": "Tom", "age": 18}

print(student["name"])
print(student.get("name"))

student["sex"]       # 键不存在会报错
student.get("sex")   # 键不存在返回 None

student.get("sex", "未知")

student = {"name": "Tom", "age": 18}

student["score"] = 90     # 新增
student["age"] = 20       # 修改
del student["name"]       # 删除

student = {"name": "Tom", "age": 18}

for key in student:
    print(key, student[key])

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

for key in student.keys():
    print(key)

for value in student.values():
    print(value)

s = "banana"
d = {}

for ch in s:
    d[ch] = d.get(ch, 0) + 1

print(d)

{'b': 1, 'a': 3, 'n': 2}

d[x] = d.get(x, 0) + 1

s = {1, 2, 3, 3, 3}
print(s)  # {1, 2, 3}

lst = [1, 2, 2, 3, 3, 3]
lst = list(set(lst))
print(lst)

s = {1, 2, 3}
# s[0]  错误

def 函数名(参数):
    函数体
    return 返回值

def add(a, b):
    return a + b

result = add(3, 5)
print(result)

def test():
    return 1
    print("hello")  # 不会执行

def hello():
    print("hello")

x = hello()
print(x)

def add(a, b):
    return a + b

add(1, 2)

def greet(name="同学"):
    print("你好", name)

greet()
greet("Tom")

def info(name, age):
    print(name, age)

info(age=18, name="Tom")

x = 10

def f():
    x = 20
    print(x)

f()        # 20
print(x)   # 10

x = 10

def f():
    global x
    x = 20

f()
print(x)  # 20

def fact(n):
    if n == 1:
        return 1
    return n * fact(n - 1)

print(fact(5))  # 120

f = open("test.txt", "r", encoding="utf-8")
content = f.read()
f.close()

with open("test.txt", "r", encoding="utf-8") as f:
    content = f.read()

with open("test.txt", "r", encoding="utf-8") as f:
    data = f.read()
    print(data)

with open("test.txt", "r", encoding="utf-8") as f:
    for line in f:
        print(line.strip())

with open("test.txt", "w", encoding="utf-8") as f:
    f.write("hello\n")
    f.write("world\n")

with open("test.txt", "a", encoding="utf-8") as f:
    f.write("new line\n")

try:
    x = int(input("请输入数字："))
    print(10 / x)
except ValueError:
    print("输入的不是整数")
except ZeroDivisionError:
    print("不能除以 0")
else:
    print("没有异常时执行")
finally:
    print("无论是否异常都会执行")

class Student:
    def __init__(self, name, age):
        self.name = name
        self.age = age

    def say_hello(self):
        print("我叫", self.name)

s1 = Student("Tom", 18)
s1.say_hello()

self.name = name

def __init__(self, name, age):
    self.name = name
    self.age = age

s = Student("Tom", 18)

class Student:
    school = "江苏大学"   # 类属性

    def __init__(self, name):
        self.name = name   # 实例属性

lst = [3, 1, 4, 2]

print(len(lst))     # 4
print(sum(lst))     # 10
print(max(lst))     # 4
print(min(lst))     # 1
print(sorted(lst))  # [1, 2, 3, 4]

n = int(input("请输入一个整数："))

if n <= 1:
    print("不是素数")
else:
    flag = True
    for i in range(2, n):
        if n % i == 0:
            flag = False
            break

    if flag:
        print("是素数")
    else:
        print("不是素数")

n = int(input("请输入一个整数："))

if n <= 1:
    print("不是素数")
else:
    flag = True
    for i in range(2, int(n ** 0.5) + 1):
        if n % i == 0:
            flag = False
            break

    print("是素数" if flag else "不是素数")

for n in range(2, 101):
    flag = True
    for i in range(2, int(n ** 0.5) + 1):
        if n % i == 0:
            flag = False
            break
    if flag:
        print(n, end=" ")

for n in range(100, 1000):
    a = n // 100
    b = n // 10 % 10
    c = n % 10

    if a ** 3 + b ** 3 + c ** 3 == n:
        print(n)

n = int(input("请输入整数："))
rev = 0

while n > 0:
    digit = n % 10
    rev = rev * 10 + digit
    n //= 10

print(rev)

a = int(input())
b = int(input())

m = min(a, b)
for i in range(m, 0, -1):
    if a % i == 0 and b % i == 0:
        print(i)
        break

a = int(input())
b = int(input())

while b != 0:
    a, b = b, a % b

print(a)

a = int(input())
b = int(input())

x, y = a, b
while b != 0:
    a, b = b, a % b

gcd = a
lcm = x * y // gcd
print(lcm)

n = int(input("请输入项数："))

a, b = 0, 1
for i in range(n):
    print(a, end=" ")
    a, b = b, a + b

lst = [5, 3, 8, 1, 2]

for i in range(len(lst) - 1):
    for j in range(len(lst) - 1 - i):
        if lst[j] > lst[j + 1]:
            lst[j], lst[j + 1] = lst[j + 1], lst[j]

print(lst)

lst = [10, 20, 30, 40]
target = int(input("请输入要查找的数："))

pos = -1
for i in range(len(lst)):
    if lst[i] == target:
        pos = i
        break

if pos == -1:
    print("没找到")
else:
    print("下标是", pos)

lst = [3, 9, 2, 9, 5]
max_value = lst[0]
max_index = 0

for i in range(1, len(lst)):
    if lst[i] > max_value:
        max_value = lst[i]
        max_index = i

print(max_value, max_index)

nums = input().split()
nums = [int(x) for x in nums]
print(sum(nums))

nums = list(map(int, input().split()))
print(sum(nums))

a = 3
b = 5
a, b = b, a
print(a, b)

a = [1, 2, 3]
b = a
b[0] = 100
print(a)

[100, 2, 3]

b = a.copy()
# 或
b = a[:]

def f(lst):
    lst.append(4)

nums = [1, 2, 3]
f(nums)
print(nums)

[1, 2, 3, 4]

print(0 and 5)   # 0
print(1 and 5)   # 5
print(0 or 5)    # 5
print(1 or 5)    # 1

print(0.1 + 0.2)

0.30000000000000004

abs((0.1 + 0.2) - 0.3) < 1e-9

def f(x, lst=[]):
    lst.append(x)
    return lst

print(f(1))
print(f(2))

[1]
[1, 2]

def f(x, lst=None):
    if lst is None:
        lst = []
    lst.append(x)
    return lst

n = int(input())

nums = list(map(int, input().split()))

n = int(input())
nums = []
for i in range(n):
    nums.append(int(input()))

n = int(input())
nums = list(map(int, input().split()))

for x in nums:
    print(x)

for i, x in enumerate(nums):
    print(i, x)

d = {}
for x in nums:
    d[x] = d.get(x, 0) + 1

nums.sort()

nums = sorted(nums)

a = input()
b = input()
print(a + b)

a = int(input())
b = int(input())
print(a + b)

for i in range(1, 10):
    print(i)

for i in range(1, 11):
    print(i)

lst = [1, 2, 3]
print(lst[3])  # 错误

d = {"a": 1}
print(d["b"])  # KeyError

print(d.get("b", 0))

i = 1
while i <= 5:
    print(i)

i = 1
while i <= 5:
    print(i)
    i += 1

for i in range(1, 101):
    if i % 3 == 0:
        print(i)

s = input()
print(s.count("a"))

nums = list(map(int, input().split()))

print(max(nums))
print(min(nums))
print(sum(nums) / len(nums))

s = input()
d = {}

for ch in s:
    d[ch] = d.get(ch, 0) + 1

print(d)

s = input()

if s == s[::-1]:
    print("是回文")
else:
    print("不是回文")

# 输入
x = int(input())
nums = list(map(int, input().split()))

# 输出
print(x)
print(a, b, sep="-", end=" ")

# 分支
if 条件:
    pass
elif 条件:
    pass
else:
    pass

# 循环
for i in range(n):
    pass

while 条件:
    pass

# 函数
def f(a, b):
    return a + b

# 列表
lst = []
lst.append(1)
lst.sort()

# 字典
d = {}
d[key] = value
d[key] = d.get(key, 0) + 1

# 文件
with open("a.txt", "r", encoding="utf-8") as f:
    data = f.read()