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使用布尔标志、逻辑和缩进错误跳出python for循环

break boolean loops list python

-2

Compoot · 技术社区 · 7 年前

下面的代码试图搜索用户名列表,并在第一次输出时返回输出“foundinindex I”或“Sorry username not Found”。

usernames=["u1","u2","u3"]
found=False

while found==False:
  username=input("Enter username:")
  for i in range(len(usernames)):
    if username==usernames[i]:
      found=True
      break

if found==True:
  print("Username found in index:",i)
else:
  print("Sorry,username not found")

如果用户名是正确的,那么当前的代码似乎可以工作,但是如果使用了错误的数据,例如23234,那么它会重复这个问题,而不会跳转到代码底部的if语句(这就是我想要的)。

有人能纠正这个代码,并解释一下解决这个问题的最有效方法。这很可能与布尔标志“found”有关,我不明白它为什么不跳出并转到if语句的底部。提前谢谢

5 回复 | 直到 7 年前

1

Manuel Fedele 7 年前

你真的需要 while 阻止?

usernames=["u1","u2","u3"]
index = 0
found = False

username = input("Enter username:")
for i in range(len(usernames)):
  if username == usernames[i]:
    found = True
    index = i
    break

if found:
  print("Username found in index:",index)
else:
  print("Sorry,username not found")

2

1

DirtyBit 7 年前

usernames=["u1","u2","u3"]

while True:
  user = input("Enter username: ")    
  if user in usernames:
    print("Username found at Index: {}".format(usernames.index(user)))
    break
  else:
    print("Sorry, username not found. Try again")

编辑

但如果您必须继续使用当前的for循环方法,请在外部for循环上放置else块,并在找到时中断:

usernames = ["u1","u2","u3"]
found = False

while found == False:
  username = input("Enter username: ")
  for i in range(len(usernames)):
    if username == usernames[i]:
        print("Username found at Index: {}".format(i))
        break
  else: # not and indentation error
        print("Sorry, username not found. Try again")

编辑2

usernames = ["u1","u2","u3"]

while True:
  username = input("Enter username: ")
  for i in range(len(usernames)):
    if username == usernames[i]:
        print("Username found at Index: {}".format(i))
        break
  else: # not and indentation error
        print("Sorry, username not found. Try again")

输出 (在所有情况下):

Enter username: 2334
Sorry, username not found. Try again
Enter username: u2
Username found at Index: 1

3

0

RedX 7 年前

if 如果输入了正确的用户名。

while found == true 位)。

或者你只问一次,看看是否找到了,因为你需要移除 找到时==真 部分。

我知道你的意思可能是迪特比特干的: https://stackoverflow.com/a/55183057

4

0

Vindicar 7 年前

while found==False: 循环到 found 变成 True .

另外,如果您想查看列表中是否存在字符串,只需使用 list.index() method :

username=input("Enter username:")
try:
    i = usernames.index(username)
except ValueError:
    print("Sorry,username not found")
else:
    print("Username found in index:",i)

5

0

Cosmin 7 年前

更好的版本是这个

usernames = ["u1", "u2", "u3"]

while True:
    username = input("Enter username:")

    if username in usernames:
        print("Username found in index:", usernames.index(username))
        break
    else:
        print("Sorry,username not found")

按要求编辑:

usernames = ["u1", "u2", "u3"]
found = False

while found is False:
    found = False
    username = input("Enter username:")

    for i in range(len(usernames)):
        if usernames[i] == username:
            print("Username found in index:", i)
            found = True
            break

    if found is False:
        print("Sorry,username not found")