Question

我编写了这个程序，以便能够从用户输入中找到A / U和C / G对的数量。当我运行它时，它会一直说“无效语法”，同时在红色的while循环后突出显示第一个“else：”。任何人都知道我需要改变什么来解决它？

def main():

    first = input("Please enter the RNA sequence for which you wish to find the number of pairs. \nFirst line:")
    second = input("Second String:")

    a1base = first.count('A')
    u1base = first.count('U')
    c1base = first.count('C')
    g1base = first.count('G')
    a2base = second.count('A')
    u2base = second.count('U')
    c2base = second.count('C')
    g2base = second.count('G')

    while (a1base >= 1) and (u1base >= 1) or (a2base >= 1) and (u2base >= 1):
        abases = (a1base+ a2base)
        ubases = (u1base + u2base)
        firstset = min(abases, ubases)
        print("You have", firstset,"A/U bases.")
        else:
            print("You have zero A/U bases.")

    while (c1base >= 1) and (g1base >= 1) or (c2base >= 1) and (g2base >= 1):
        cbases = (c1base + c2base)
        gbases = (g1base + g2base)
        secondset = min(cbases, gbases)
        print("You have", secondset,"C/G bases.")
        else:
            print("You have zero C/G bases.")



main()

Answer 1

您有else:未附加到任何if，for，while或try声明，这是非法的。

如果你想将else附加到while，解决方法很简单：更改缩进以附加它：

while (a1base >= 1) and (u1base >= 1) or (a2base >= 1) and (u2base >= 1):
    abases = (a1base+ a2base)
    ubases = (u1base + u2base)
    firstset = min(abases, ubases)
    print("You have", firstset,"A/U bases.")
else:
    print("You have zero A/U bases.")

请参阅教程中的break and continue Statements, and else Clauses on Loops（以及语言参考中的Compound statements以获取完整详情。）

Answer 2

您的else需要缩进到与while相同的级别，在这种情况下这是没有意义的，因为您的循环中没有break，或者您需要在它之前的某一行添加if。

Answer 3

我看到两件显而易见的事情：

def main():之后的所有内容都应缩进;
Else应与while处于同一级别的缩进。它不是孩子，而是while的兄弟姐妹。

Answer 4

其他人已经解释了错误。

尝试将while循环更改为：

abases = (a1base+ a2base)
ubases = (u1base + u2base)
firstset = min(abases, ubases)
print("You have", firstset if firstset else 'zero',"A/U bases.")

cbases = (c1base + c2base)
gbases = (g1base + g2base)
secondset = min(cbases, gbases)
print("You have", secondset if secondset else 'zero',"C/G bases.")

没有任何while或else:。

以下代码段也应该做同样的事情：

first = input("Please enter the RNA sequence for which you wish to find the number of pairs. \nFirst line:")
second = input("Second String:")
bases = {k: (first + second).count(k) for k in 'AUCG'}
print('You have', min(bases['A'], bases['U']), 'A/U bases.')
print('You have', min(bases['C'], bases['G']), 'C/G bases.')

Python：为什么它一直说无效语法？

4 个答案: