From: Steven D'Aprano <st...@pearwood.info>
To: tutor@python.org
Sent: Tuesday, March 6, 2012 1:58 AM
Subject: Re: [Tutor] question about operator overloading
Alan Gauld wrote:
>> On 05/03/12 21:25, Dave Angel wrote:
>>
>>> It's not clear what __add__() should mean for physical files.
>>
>> My guess would be similar to the cat operator in Unix:
>>
>> $ cat file1, file2 > file3
>>
>> is equivalent to
>>
>> file3 = file1 + file2
>>
>> But of course, thats just my interpretation of file addition...
>
>I think that's what Albert-Jan is probably thinking, but the two models are
>not quite the same. I think that what he wants is probably closer to something
>like the fileinput module. I think what he wants is to avoid this:
>-----> First off, thank you all for your replies, including the replies after
>this mail. And sorry for top-posting in an earlier mail
>-----> And yes indeed Steven and Alan, this is what I had in mind.
>for f in (file1, file2, file3, file4):
> for record in f:
> process(record)
>
>in favour of this:
>
>all_the_files = file1 + file2 + file3 + file4 # merge file contents
>for record in all_the_files:
> process(record)
>
>Albert-Jan, am I close? If not, please explain what you are trying to
>accomplish.
>----> What I had in mind was something like Peter Otten suggested:
>merged = file1 + file2
>merged.save_as(filename)
>Your solution looks intuitive, but won't "all_the_files" become very large if
>file1 through file4 contain, say, 100 billion values each?
>
>If the files are small, the easy way is to just read their contents, add them
>together as strings or lists, and then process the lot. But if the files are
>big, or you want to process them on-demand instead of up-front, you need an
>approach similar to fileinput.
>----> see above. Btw, contrary to what somebody in this thread said, Spss
>files are binary files, not text files.
>
>Personally, all these Reader and Append objects make my brain hurt, and I
>hardly ever use operator overloading, except perhaps for numeric types. Reader
>objects, I can just get. But "Append" objects?
>
>This may be useful:
>
>http://steve-yegge.blogspot.com.au/2006/03/execution-in-kingdom-of-nouns.html
>----> Nice one ;-))
>
>and also itertools:
>
>
>from itertools import chain
>merged = chain(file1, file2, file3, file4)
>for record in merged:
> process(record)
>----> Very, *very* useful function, thank you!
>----> this is (incomplete) code that I created without bothering about __add__:
>with SavWriter(mergedSavFileName, varNames, varTypes) as sav_merged:
> for savFileName in glob.glob("d:/temp/*.sav"):
> with SavReader(savFileName) as sav_r:
> header = sav_r.next()
> for row in sav_r:
> sav_merged.writerow(row)
>http://code.activestate.com/recipes/577811-python-reader-writer-for-spss-sav-files-linux-mac-/
>---> Maybe I am making my life too difficult by trying to use __add__?
>
>-- Steven
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