python – 动态构建布尔表达式

朴素版：

prefix = 'hello0'
while os.path.exists(prefix + '.abc') or os.path.exists(prefix + '.def') or os.path.exists(prefix + '.ghi'):
    n = int(prefix[-1])
    prefix = prefix[:-1] + str(n + 1)  # I know this doesn't work when n reaches two digits; my full code involves a regular expression

当有超过几个扩展时,这种情况显然会变得非常漫长和丑陋.我把它抽象为for循环.

我的版本：

prefix = 'hello0'
extensions = ('.abc','.def','.ghi')  # there could be even more than this
condition = True
while condition:
    condition = False
    # if any of the paths still exist,set the condition back to True
    for extension in extensions:
        if os.path.exists(prefix + extension):
            condition = True

    n = int(prefix[-1])
    prefix = prefix[:-1] + str(n + 1)

我仍然觉得这有点笨拙：还不完全清楚while循环实际上是在测试什么.是否可以动态构建布尔表达式,而不是设置布尔值？

我认为以下可能有用(我没有测试过,我只是在写这篇文章的时候才想到它！)但是我认为我不应该求助于eval：

prefix = 'hello0'
extensions = ('.abc','.ghi')

test = 'False'
for extension in extensions:
    test += " or os.path.exists(prefix + '" + extension + "')"
while eval(test):
    n = int(prefix[-1])
    prefix = prefix[:-1] + str(n + 1)