On 11/2/2011 7:06 PM, Dennis Lee Bieber wrote:
On Wed, 2 Nov 2011 14:13:34 -0700 (PDT), Matt<macma...@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
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