Working with Huge Text Files
mensanator at aol.com
mensanator at aol.com
Sat Mar 19 01:57:00 CET 2005
Lorn Davies wrote:
> Hi there, I'm a Python newbie hoping for some direction in working
> text files that range from 100MB to 1G in size. Basically certain
> sorted by the first (primary) field maybe second (date), need to be
> copied and written to their own file, and some string manipulations
> need to happen as well. An example of the current format:
> | followed by like a million rows similar to the above, with
> | incrementing date and time, and then on to next primary field
> | etc., there are usually 10-20 of the first field per file
> | so there's a lot of repetition going on
> The export would ideally look like this where the first field would
> written as the name of the file (XYZ.txt):
> 19930104, 93027, 2887, 7600, 40, 0, Z, N
> Pretty ambitious for a newbie? I really hope not. I've been looking
> simpleParse, but it's a bit intense at first glance... not sure where
> to start, or even if I need to go that route. Any help from you guys
> what direction to go or how to approach this would be hugely
> Best regards,
You could use the csv module.
Here's the example from the manual with your sample data in a file
reader = csv.reader(file("some.csv"))
for row in reader:
['XYZ', '04JAN1993', '9:30:27', '28.87', '7600', '40', '0', 'Z', 'N ']
['XYZ', '04JAN1993', '9:30:28', '28.87', '1600', '40', '0', 'Z', 'N ']
['ABC', '04JAN1993', '9:30:27', '28.875', '7600', '40', '0', 'Z', 'N ']
The csv module while bring each line in as a list of strings.
Of course, you want to process each line before printing it.
And you don't just want to print it, you want to write it to a file.
So after reading the first line, open a file for writing with the
first field (row) as the file name. Then you want to process
fields row, row and row to get them in the right format
and then write all the row fields except row to the file that's
open for writing.
On every subsequent line you must check to see if row has changed,
so you'll have to store row in a variable. If it's changed, close
the file you've been writing to and open a new file with the new
row. Then continue processing lines as before.
It will only be this simple if you can guarantee that the original
file is actually sorted by the first field.
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