Python - 使用readlines处理第n行跳转（）

Question

I'm having a go at a fixing a broken lib that I want to use on Github.

I have locally "fixed" the problem. but I don't think its a very clean method...

I'm poking the WARC library by the internet archive, and spcifically the arc.py part ( https://github.com/internetarchive/warc/blob/master/warc/arc.py ).

Since the lib was written, the tools that make the ARC files have changed a bit, and as a result, the builtin parser fails, as its not expecting to see some metadata in the file.

My local fix looks like this:

    if header.startswith("<arcmetadata"):
        while not header.endswith("</arcmetadata>\n"):
            header = self.fileobj.readline()
        header = self.fileobj.readline()
        header = self.fileobj.readline()

And I'm not sure that my calling of readlines() twice to strip of the next two empty lines (containing "/n" is the cleanest way of advancing through the fileobject.

Is this good python? or is there a better way?

Answer 1

The code looks like a copy/paste error. There is nothing wrong with using .readline() , just document what you are doing:

# skip metadata
if header.startswith("<arcmetadata"):
    while not header.endswith("</arcmetadata>\n"):
        header = self.fileobj.readline()
    #NOTE: header ends with `"</arc..."` here i.e., it is not blank

# skip blank lines
while not header.strip():
    header = self.fileobj.readline()

btw, if the file contains xml then use an xml parser to parse it. Don't do it by hand.

Answer 2

Although there's nothing inherently wrong with what you're doing, it might be more semantic to write:

next(self.fileobj, None)

without a variable assignment to signify that you are tossing the next line.

Answer 3

itertools may be of use here

from itertools import islice, dropwhile
if header.startswith("<arcmetadata"):
    fileobj = dropwhile(lambda x: not x.endswith("</arcmetadata>\n"), fileobj)
    fileobj = islice(fileobj, 2, None)