Python - 测试Raw-Input是否没有条目

Question

我有可能是最愚蠢的问题......

如何判断raw_input是否从未输入任何内容？(空值)

final = raw_input("We will only cube numbers that are divisible by 3?")
if len(final)==0:
    print "You need to type something in..."
else:
    def cube(n):
        return n**3
    def by_three(n):
        if n%3==0:
            return cube(n)
        else:
            return "Sorry Bro. Please enter a number divisible by 3"
    print by_three(int(final))

特别是2号线...如果最终没有输入,我将如何测试？对于输入的任何内容,代码都可以正常工作,但如果没有提供输入则会中断....

我确信这很简单,但任何帮助都表示赞赏.

Answer 1

没有条目导致空字符串; 空字符串(如空容器和数字零)测试为布尔值false; 只需测试not final:

if not final:
    print "You need to type something in..."

您可能希望删除所有空格的字符串,以避免在仅输入空格或制表符时断开:

if not final.strip():
    print "You need to type something in..."

但是,您仍需要验证用户是否输入了有效的整数.您可以捕获ValueError异常:

final = raw_input("We will only cube numbers that are divisible by 3?")
try:
    final = int(final)
except ValueError:
    print "You need to type in a valid integer number!"
else:
    # code to execute when `final` was correctly interpreted as an integer.