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Question

我正在尝试实现类似于ansible with_first_found的东西，

configuration = {
   "fedora-27"    : "edge-case options for fedora 27",
   "ubuntu-14.04" : "edge-case options for ubuntu 14.04",
   "fedora"       : "as long as it's fedora, these options are fine",
   "ubuntu"       : "these options are good for all ubuntu versions",
   "redhat"       : "options for rpm distros",
   "debian"       : "try these options for anything remotely resembling debian",
   "default"      : "/if/all/else/fails",
}

if __name__ == "__main__":

   distribution_release = "ubuntu-16.04"
   distribution = "ubuntu"
   os_family = "debian"

   lookup = [
      distribution_release,
      distribution,
      os_family,
      "default"
   ]

   for key in lookup:
      if key in configuration:
         first_found = configuration[key]
         break

   print(first_found)

现在，这段代码做了我想做的事情，但我有一种感觉，有一种更好的方法来完成这种查找。这个for/if/break循环可以在一行程序中完成吗？

根据timgeb的评论，更接近我的目标。

   first_found = next(configuration[key] for key in lookup if key in configuration)

这可能有点难读。

Answer 1

您的代码没有任何问题。

您可以通过构造一个生成器并在其上调用next来缩短它。

>>> demo = {1:2, 3:4, 5:6}
>>> next(demo[k] for k in (6,3,5) if k in demo)
4

这还允许使用默认值：

>>> next((demo[k] for k in (0,-1,-2) if k in demo), 'default')
'default'