虽然python中的语句循环
我正在学习python,并且我被卡在下面的代码中的无限while循环中。虽然python中的语句循环
A = input("Hello what is your name? ")
D = input("What is today's date? ")
B = input("Did you have a good day [y/N]")
while B != "y" or B != "Y" or B != "N" or B != "n":
B = input("Did you have a good day [y/N]")
else:
if B == "Y" or B == "y":
print(A + ", ")
C = input("Tell me about your day ")
with open("Start.txt", "a") as infile:
infile.write("\n")
infile.write(A)
infile.write(" ran Start.py and said he had a good day on ")
infile.write(D)
infile.write(".")
infile.write("\n He reports today:\n ")
infile.write(C)
elif B == "N" or "n":
print(A + ", ")
C = input("Tell me about your day ")
with open("Start.txt", "a") as infile:
infile.write("\n")
infile.write(A)
infile.write(" ran Start.py and said he had a bad day on ")
infile.write(D)
infile.write(".")
infile.write("\n He reports today:\n ")
infile.write(C)
当B进行比较,看它是否等于Y,Y,N,或N 但仍然不管我给它对于B输入什么坚持我到while语句,并保持该问题发生我在那里。
的问题是,你正在做while B != "y" or B != "Y" or B != "N" or B != "n":
随着or
如果任其选择是正确返回true。因此,如果B =“N” b!="N" or b!=n"
是真正的原因是b仍然不是“N”
您可以通过and
小号更换所有的or
s到得到这个 while B != "y" and B != "Y" and B != "N" and B != "n":
的问题是在这里解决这个:
while B != "y" or B != "Y" or B != "N" or B != "n":
B
是总是不等于其中的一个。如果它是“y”,则不等于其他三个,依此类推。而且,由于您正在使用or
来合并这些条件,因此,如果任何一个条件成立,循环就会继续,正如我们所见,始终如此。
重写使用and
:
while B != "y" and B != "Y" and B != "N" and B != "n":
或应用德摩根定律(因子的not
了表达和交换and
/or
的):
while not (B == "y" or B == "Y" or B == "N" or B == "n"):
或最重要的,它写了Python方式:
while B.lower() not in "yn":
(这也接受一个空的答案,根据您的提示相当于“N”。为了解决这个问题,只需将您elif
为纯else
,没有条件。)
此行
elif B == "N" or "n":
应该
elif B == "N" or B == "n":
你应该使用条件下,只需"n"
(非空字符串)表示true
让我们使用while循环的简化版本。
while B != "Y" or B != "y":
# ...
有没有办法,这将永远评估False
。
若B被设置为Y
然后B != "Y"
将False
,但B != "y"
会True
。
我认为,在这种情况下,它可能是更清洁做类似
while B not in ["y", "Y", "n", "N"]:
# ...
然后将重复,直到输入清单中的人物之一。
编辑:有些其他答案建议使用while B not in "yYnN"
或等效。这在这里工作,因为你所有的预期回应是一个字符。如果您稍后决定接受"yes"
作为回复,那么您将不得不使用上面显示的列表。
这是最简单的解决方案!
while B not in "YNyn":