Python尝试/除了：尝试多个选项 [英] Python try/except: trying multiple options

问题描述

我正在尝试从与信息位置不一致的网页上删除一些信息。我有代码来处理几种可能性;我想要的是按顺序尝试它们，那么如果没有一个工作，我想要优雅地失败并继续前进。

I'm trying to scrape some information from webpages that are inconsistent about where the info is located. I've got code to handle each of several possibilities; what I want is to try them in sequence, then if none of them work I'd like to fail gracefully and move on.

就是说，在伪代码中：

That is, in psuedo-code:

try:
    info = look_in_first_place()
otherwise try:
    info = look in_second_place()
otherwise try:
    info = look_in_third_place()
except AttributeError:
    info = "Info not found"

我可以使用嵌套的try语句来做到这一点，但是如果我需要15种可能性，那么我需要15个级别的缩进！

I could do this with nested try statements, but if I need 15 possibilities to try then I'll need 15 levels of indentation!

这似乎是一个琐碎的问题，我觉得我错过了一些东西，但是我已经搜索到了地面，找不到与这种情况相当的任何东西。有没有一个明智的和Pythonic的方式来做到这一点？

This seems like a trivial enough question that I feel like I'm missing something, but I've searched it into the ground and can't find anything that looks equivalent to this situation. Is there a sensible and Pythonic way to do this?

编辑：正如约翰（相当不错的）下面的解决方案提出来的，为了简洁起见，我把每个查找都写成一个单一的函数调用，而实际上通常是一小块BeautifulSoup调用，例如 soup.find（'h1'，class _ ='parselikeHeader'）。当然，我可以把它们包含在这些函数中，但是这似乎有点不合适 - 如果我的速记改变了问题，那么道歉。

As John's (pretty good) solution below raises, for brevity I've written each lookup above as a single function call, whereas in reality it's usually a small block of BeautifulSoup calls such as soup.find('h1', class_='parselikeHeader'). Of course I could wrap these in functions, but it seems a bit inelegant with such simple blocks -- apologies if my shorthand changes the problem though.

这可能是一个更多的有用的说明：

This may be a more useful illustration:

try:
    info = soup.find('h1', class_='parselikeHeader').get('href')
if that fails try:
    marker = soup.find('span', class_='header')
    info = '_'.join(marker.stripped_strings)
if that fails try:
    (other options)
except AttributeError:
    info = "Info not found"

推荐答案

如果每个查找是一个单独的函数，您可以将所有函数存储在列表中，然后逐个迭代。

If each lookup is a separate function, you can store all the functions in a list and then iterate over them one by one.

lookups = [
    look_in_first_place,
    look_in_second_place,
    look_in_third_place
]

info = None

for lookup in lookups:
    try:
        info = lookup()
        # exit the loop on success
        break    
    except AttributeError:
        # repeat the loop on failure
        continue

# when the loop is finished, check if we found a result or not
if info:
    # success
else:
    # failure

这篇关于Python尝试/除了：尝试多个选项的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！