逻辑判断

用户输入判断：

1 _username='Lxxxl'
2 _password='asd123'
3 username=input("username:")
4 password=input("password:")
5 
6 if _username==username and _password==password:
7     print("Welcome user {name} login...".format(name=username))
8 else:
9     print("Invalid username or password!")

以上只能判断一次

while True:
    _username = 'Lxxxl'
    _password = 'asd123'
    username = input("username:")
    password = input("password:")

    if _username == username and _password == password:
        print("Welcome user {name} login...".format(name=username))
    else:
        print("Invalid username or password!")

一直循环  

for i in range(3):
    _username = 'Lxxxl'
    _password = 'asd123'
    username = input("username:")
    password = input("password:")

    if _username == username and _password == password:

        print("Welcome user {name} login...".format(name=username))
    else:
        print("Invalid username or password!")

循环三次，不论用户信息输入对或错

for i in range(3):
    _username = 'Lxxxl'
    _password = 'asd123'
    username = input("username:")
    password = input("password:")

    if _username == username and _password == password:
        break
        print("Welcome user {name} login...".format(name=username))
    else:
        print("Invalid username or password!")

答对结束，答错继续循环三次

count=0
while True:
    print("count:",count)
    count=count+1

      if count==1000:
      break

循环：数字从0开始+1       ,加到1000停止

Lxxxl_age=23
guess_age=int(input("Guess age:"))
if guess_age==Lxxxl_age:
    print("Yse,you got it .")
elif guess_age>Lxxxl_age:
    print("Think smaller...")
else:
    print("Think bigger!")

猜年龄  运行一次

Lxxxl_age = 23
count=0
while True:
    if count==3:                                       
        break               换成  while count<3:
    guess_age = int(input("Guess age:"))
    if guess_age == Lxxxl_age:

        print("Yse,you got it .")
        break
    elif guess_age > Lxxxl_age:
        print("Think smaller...")
    else:
        print("Think bigger!")
    count+=1

  else:
      print("You have tried too many times ...fuck off")

for i in range(3):
    Lxxxl_age = 23
    guess_age = int(input("Guess age:"))
    if guess_age == Lxxxl_age:

        print("Yse,you got it .")
        break
    elif guess_age > Lxxxl_age:
        print("Think smaller...")
    else:
        print("Think bigger!")

   else:
      print("You have tried too many times ...fuck off")

猜年龄 运行三次  如果答对结束（break要放在print后，否则直接结束，没有print）   两种方法， 第一种是计数,第二种属于优化。

for i in range(10):
    print("loop",i)

for i in range(0,10,2):
    print("loop",i)

for循环   第一个是默认从0开始，中间隔1个

Lxxxl_age = 23
count=0
while count<3:
     guess_age = int(input("Guess age:"))
     if guess_age == Lxxxl_age:

         print("Yse,you got it .")
         break
     elif guess_age > Lxxxl_age:
         print("Think smaller...")
     else:
         print("Think bigger!")
     count+=1
     if count==3:
         countine_confirm=input("Do you want to keep guessing..?")
         if countine_confirm!='n':
             count=0

如果猜错可以选择是否继续，输入n就会结束。