提高异常与返回无Python功能 [英] Raise exception vs. return None in Python functions

问题描述

Python中的用户定义函数中更好的做法是：引发异常或返回None？例如，我有一个函数可以找到文件夹中最新的文件。

  def latestpdf（folder）：
＃列出文件并对它们进行排序
 try：
 latest = files [-1] 
除了IndexError：
＃文件夹为空。 
 return None＃一种可能性
 raise FileNotFoundError（）＃Alternative 
 else：
 return somefunc（最新）＃在我的情况下，somefunc解析文件名
 
解决方案
这是一个语义问题。  foo = latestpdf（d） 意味着？
 
 
 
没有最新的文件？那么确定，只要返回None。
 
 
 
您是否期望总是找到最新的文件？提出例外。是的，重新提出一个更合适的例外是很好的。
 
 
 
如果这只是一个应用于任何目录的通用函数，我会做前者和返回无。如果目录是例如意图是包含应用程序已知文件集的特定数据目录，我会引发一个例外。
 
What's better practice in a user-defined function in Python: raise an exception or return None?  For example, I have a function that finds the most recent file in a folder.
def latestpdf(folder):
    # list the files and sort them
    try:
        latest = files[-1]
    except IndexError:
        # Folder is empty.
        return None  # One possibility
        raise FileNotFoundError()  # Alternative
    else:
        return somefunc(latest)  # In my case, somefunc parses the filename
Another option is leave the exception and handle it in the caller code, but I figure it's more clear to deal with a FileNotFoundError than an IndexError.  Or is it bad form to re-raise an exception with a different name?
解决方案
It's really a matter of semantics.  What does foo = latestpdf(d) mean?

Is it perfectly reasonable that there's no latest file?  Then sure, just return None.

Are you expecting to always find a latest file?  Raise an exception.  And yes, re-raising a more appropriate exception is fine.

If this is just a general function that's supposed to apply to any directory, I'd do the former and return None.  If the directory is, e.g., meant to be a specific data directory that contains an application's known set of files, I'd raise an exception.

                        
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