[Tutor] compare and arrange file

[Edgar Almonte]

On Tue, Jul 12, 2011 at 10:32 PM, Emile van Sebille <emile at fenx.com> wrote:
> On 7/12/2011 4:01 PM Edgar Almonte said...
>>
>> On Tue, Jul 12, 2011 at 5:44 AM, Peter Otten<__peter__ at web.de>  wrote:
>
> <snip>
>>>
>>> import csv
>
> imports the comma separated values (csv) file handler utilities module
>
>>>
>>> def sortkey(row):
>>>    if float(row[1]):
>>>        return row[1], True
>>>    else:
>>>        return row[2], False
>
> ... sortkey defines a function that accepts a cvs.reader data row, and
> returns either row[1] and True or row[2] and False based on which of row[1]
> and row[2] has a non-zero value
>
>>>
>>> with open("infile.txt", "rb") as instream:
>>>    rows = sorted(csv.reader(instream, delimiter="|"), key=sortkey)
>
> rows becomes the sortkey sorted result of the lines of infile.txt
>
>>>
>>> with open("outfile.txt", "wb") as outstream:
>>>    csv.writer(outstream, delimiter="|").writerows(rows)
>
> ... and this writes those results to outfile.txt
>
> you might also try the shortened:
>
> from csv import reader,writer
>
> def sortkey(row): return max(row[1],row[2]),row[1]>row[2]
>
> writer(open("outfile.txt", "wb"), delimiter="|").writerows(
> sorted(reader(open("infile.txt", "rb"), delimiter="|"),key=sortkey))
>
>
> Emile
>
> _______________________________________________
> Tutor maillist  -  Tutor at python.org
> To unsubscribe or change subscription options:
> http://mail.python.org/mailman/listinfo/tutor
>

fist time i saw the statement "with" , is part of the module csv ? ,
that make a loop through the file ? is not the sortkey function
waiting for a paramenter ( the row ) ? i don't see how is get pass ,
the "key" is a parameter of sorted function ? , reader is a function
of csv module ? if "with..." is a loop  that go through the file is
the second with inside of that loop ? ( i dont see how the write of
the output file catch the line readed

Thanks again for the helping of my understand