continue vs. pass in this IO reading and writing

kbtyo ahlusar.ahluwalia at gmail.com
Thu Sep 3 17:49:43 CEST 2015


On Thursday, September 3, 2015 at 11:27:58 AM UTC-4, Chris Angelico wrote:
> On Fri, Sep 4, 2015 at 1:05 AM, kbtyo 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").


So what I hear you saying is I am not entering the else" block? Hence, when each file is read, the rest of the suite is not applied - specifically, 

   if not header_saved:
       fout.write(header)
       header_saved = True
       print("We got here")

> 
> 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

Would you mind elaborating on what you meant by "compatible headers"? I have files that may have different headers. If they are different, they should be appended (along with their values). If there are duplicate headers, then their values should just be added. 





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