引发异常与返回在函数中无？ [英] Raise exception vs. return None in functions?

问题描述

在Python中的用户定义函数中，更好的做法是：引发异常或不返回？例如，我有一个函数可以找到文件夹中的最新文件。

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

另一个选择是保留异常并在调用方代码中处理它，但我认为处理<$ c $更清楚c> FileNotFoundError 比 IndexError 。还是用其他名称重新引发异常是不好的形式吗？

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?

推荐答案

这实际上是语义问题。 foo = Latestpdf（d） 平均值是什么？

It's really a matter of semantics. What does foo = latestpdf(d) mean?

没有最新文件？然后确定，只返回None。

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

您是否希望总是找到最新文件？引发异常。是的，重新引发一个更合适的异常是可以的。

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

如果这只是应该应用于任何目录的通用函数，我会做一个不返回。如果该目录是（例如）要成为包含应用程序已知文件集的特定数据目录，则将引发异常。

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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