常用语句

# 常用语句

## 条件语句

### if.....else....

while True:
    x = int(input("请输入数字:50"))
    if x >50:
        print("你输入的数大于50")
    else:
        print("你输入的值小于50")



### if....elif....else...

while True:
    x = int(input("请输入数字:"))
    if x >90:
        print("你输入的数大于90")
    elif x >80:
        print("你输入的值大于80")
    elif x > 70:
        print("你输入的值大于70")



## continue

### 条件满足调到while循环语句

i =10
while i >0:
    i -= 1
    if i==5:
        continue
    print(i)
结果:
9
8
7
6
4
3
2
1
0


## break

### 条件满足跳出循环

i =10
while True:
    i -= 1
    if i==5:
        break
    print(i)
结果:
9
8
7
6


## return

### 函数返回,可带返回值,返回值可以是元祖,无需加括号,可不带

def func2(b):
    return b **2


print(func2(3))
结果:
9


## 循环语句

### while...

while True:
    x = input("请输入数字:")
    if len(x)>0 and x.isdigit():  #判断是否空也可以用bool如下:if not len(x) and x.isdigit():
        x1 = int(x)
    # if x.isdecimal():
    #     x1 = int(x)
    # else:
    #     print("你输入的不是数字")
        if x1 >90:
            print("你输入的数大于90")
        elif x1 >80:
            print("你输入的值大于80")
        elif x1 > 70:
            print("你输入的值大于70")
        elif x1 == 0:
            break

    else:
        print("你输入为空,或者输入的不是数字")



### while...else...

- while条件不满足就执行else

  age_old_boy = 40
  count = 0
  while count < 3:
      guess_age = int(input("请输入年龄>>> "))
      if guess_age == age_old_boy:
          print("猜对了")
          break
      elif guess_age > age_old_boy:
          print("猜大了!")
      else:
          print("猜小了!")
      count += 1
  else:
      print("次数到了,滚蛋!")
  不执行while 就执行else
  
  

### for....in...:

x1 = [‘我‘,1,{‘姓名‘:"林明均","年龄":10},(1,"年级")]
for item in x1:
    print(item)
结果:

1
{‘姓名‘: ‘林明均‘, ‘年龄‘: 10}
(1, ‘年级‘)


### for ...else......

- 循环执行for里面的循环,完了执行else,如果不想执行else,就在for里面用break,就跳过else

  def login(self,dic):
      """
      从文件里面获取用户密码,并比较后,发回比较结果
      :param dic:
      :return:
      """
      with open("info.txt",mode="r",encoding="utf-8") as f:
          for line in f:
              username,password = line.strip().split("|")
              if username==dic["username"] and password==dic["password"]:
                  flag = 1
                  break
          else:
              flag = 0
      dic = {"operate":"login","result":flag}
      return dic
  
  

## 三目运算符/三元表达式

### 为真时的结果 if 判断条件  else  为假时的结果

# x1 = 20
# result = x1+2 if x1 > 10 else x1**2
# print(result)

# def fn(n):
#     return n+1 if n%2 ==1 else n
# print(fn(3))






## lamda表达式,只是定义了函数,必须调用才执行

func = lambda x: x*x
print(func(3))

结果:
9

列2:

fib=lambda n,x=0,y=1:x if n>5 else y
print([fib(i)  for i in range(10)])
结果:
[1, 1, 1, 1, 1, 1, 0, 0, 0, 0]


## 推导式

### 列表推导式


列1:
print([i**2  for i in range(10)])
结果:
[0, 1, 4, 9, 16, 25, 36, 49, 64, 81]

列2:
print([i**2  for i in range(10) if i%2 is 0])
结果:
[0, 4, 16, 36, 64]
例3:

def squared(x):
    return x*x
multiples = [squared(i) for i in range(30) if i % 3 is 0]

print(multiples)
结果:
[0, 9, 36, 81, 144, 225, 324, 441, 576, 729]


### 字典推导式

mcase = {‘a‘: 10, ‘b‘: 34}
mcase_frequency = {mcase[k]: k for k in mcase}
print(mcase_frequency)
结果:
{10: ‘a‘, 34: ‘b‘}

例2

dic = {"k"+str(i):i for i in range(5)}
print(dic)
结果:
{‘k0‘: 0, ‘k1‘: 1, ‘k2‘: 2, ‘k3‘: 3, ‘k4‘: 4}


### 集合推导式

squared = {x**2 for x in [1, 2, 3]}
print(squared)


结果:
{1, 4, 9}


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常用语句

原文地址:https://www.cnblogs.com/shalaotou/p/14650624.html