判断、循环

• 布尔表达式

# 相等
== 
# 不等
!= 
# 大于
>
# 大于等于
>=
# 小于
< 
# 小于等于
<=
# 连写
2 < num <= 5
num > 2 and num <=5
# 且
表达式1  and  表达式2
# 或
表达式1  or  表达式2
# 非
not 表达式1

• 判断语句

# 写法1
if len(phone) > 11:
    print('输入正确')

# 写法2
if len(phone) > 11:
    print('输入错误')
else:
    print('输入正确')  

# 写法3
if len(phone) > 11:
    print('输入错误')
elif phone.isdigit(): 
    print('输入错误')
else:
    print('输入正确') 

# 使用return
a=12
def test():
    if  a < 11:
        print('输入错误')
        return 11
    elif a > 22:
        print('输入错误')
        return 22
    else:
        print('输入正确')
        return 33
b = test()
print(b)

# 使用return
a=12
def test():
    if  a < 11:
        print('输入错误')
    elif a > 22:
        print('输入错误')
    else:
        print('输入正确')
    return a
b = test()
print(b)

• while循环

while 条件为true时:
    // 循环体

i = 1
while i <= 100:
    print(i)
    i += 1

• for循环

list= [123, 456]
for a in list:
    print(a)

• range函数

# 从0到99
for n in range(100):  
    print(n) 

# 从指定数开始
for n in range(50,101):  
    print(n) 

# 指定步长
for n in range(50,101,5):  
    print(n) 

• enumerate函数

# 获取列表中的每个元素及索引
list = ['aaa', 'bbb', 'ccc']
for idx, a in enumerate(list):
    print(f'{idx},{a}')

• break终止循环

while True:
    command = input("请输入命令:")
    if command == 'exit':
        break
    print(f'输入的命令是{command}')
print('程序结束')

for i in range(100):
    command = input("请输入命令:")
    if command == 'exit':
        break
    print(f'输入的命令是{command}')
print('程序结束')

• continue结束当前这一轮的循环

while True:
    command = input("请输入命令:")
    if command == 'exit':
        break
    if command == 'cont':
        continue
    print(f'输入的命令是{command}')
print('程序结束')

• 列表推导式

list1 = [1,2,3,4,5,6]
list2 = []
for num in list1:
    list2.append(num*num)

list1 = [1,2,3,4,5,6]
list2 = [num**2 for num in list1]

• 循环嵌套

list1 = ['关羽','张飞','赵云','马超','黄忠']
list2 = ['典韦','许褚','张辽','夏侯惇','夏侯渊']
for member1 in list1:
    for member2 in list2:
        print(f'{member1} 大战 {member2}')