simple file flow question with csv.reader

[Jon Clements]

On Nov 2, 11:50 pm, Terry Reedy <tjre... at udel.edu> wrote:
> On 11/2/2011 7:06 PM, Dennis Lee Bieber wrote:
>
> > On Wed, 2 Nov 2011 14:13:34 -0700 (PDT), Matt<macma... at gmail.com>
> > declaimed the following in gmane.comp.python.general:
>
> >> I have a few hundred .csv files, and to each file, I want to
> >> manipulate the data, then save back to the original file.
>
> That is dangerous. Better to replace the file with a new one of the same
> name.
>
> > Option 1:  Read the file completely into memory (your example is
> > reading line by line); close the reader and its file; reopen the
> > file for "wb" (delete, create new); open CSV writer on that file;
> > write the memory contents.
>
> and lose data if your system crashes or freezes during the write.
>
> > Option 2:  Open a temporary file "wb"; open a CSV writer on the file;
> > for each line from the reader, update the data, send to the writer;
> > at end of reader, close reader and file; delete original file;
> > rename temporary file to the original name.
>
> This works best if new file is given a name related to the original
> name, in case rename fails. Alternative is to rename original x to
> x.bak, write or rename new file, then delete .bak file.
>
> --
> Terry Jan Reedy

To the OP, I agree with Terry, but will add my 2p.

What is this meant to achieve?

>>> row = range(10)
>>>
print ">",row[0],row[4],"\n",row[1], "\n", ">", row[2], "\n", row[3]
> 0 4
1
> 2
3

Is something meant to read this afterwards?

I'd personally create a subdir called db, create a sqlite3 db, then
load all the required fields into it (with a column for filename)...
it will either work or fail, then if it succeeds, start overwriting
the originals - just a "select * from some_table" will do, using
itertools.groupby on the filename column, changing the open() request
etc...

just my 2p mind you,

Jon.