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Date: Fri, 4 Sep 2015 01:27:13 +1000
Subject: Re: continue vs. pass in this IO reading and writing
From: Chris Angelico <rosuav@gmail.com>
Cc: "python-list@python.org" <python-list@python.org>
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On Fri, Sep 4, 2015 at 1:05 AM, kbtyo <ahlusar.ahluwalia@gmail.com> wrote:
> However, I am uncertain as to how this executes in a context like this:
>
> import glob
> import csv
> from collections import OrderedDict
>
> interesting_files = glob.glob("*.csv")
>
> header_saved = False
> with open('merged_output_mod.csv','w') as fout:
>
>     for filename in interesting_files:
>         print("execution here again")
>         with open(filename) as fin:
>             try:
>                 header = next(fin)
>                 print("Entering Try and Except")
>             except:
>                 StopIteration
>                 continue

I think what you want here is:

except StopIteration:
    continue

The code you have will catch _any_ exception, and then look up the
name StopIteration (and discard it).

>             else:
>                 if not header_saved:
>                     fout.write(header)
>                     header_saved = True
>                     print("We got here")
>                 for line in fin:
>                     fout.write(line)
>
> My questions are (for some reason my interpreter does not print out any readout):
>
> 1. after the exception is raised does the continue return back up to the beginning of the for loop (and the "else" conditional is not even encountered)?
>
> 2. How would a pass behave in this situation?

The continue statement means "skip the rest of this loop's body and go
to the next iteration of the loop, if there is one". In this case,
there's no further body, so it's going to be the same as "pass" (which
means "do nothing").

For the rest, I think your code should be broadly functional. Of
course, it assumes that your files all have compatible headers, but
presumably you know that that's safe.

ChrisA