How do I split a huge text file in python

Question

I have a huge text file (~1GB) and sadly the text editor I use won't read such a large file. However, if I can just split it into two or three parts I'll be fine, so, as an exercise I wanted to write a program in python to do it.

What I think I want the program to do is to find the size of a file, divide that number into parts, and for each part, read up to that point in chunks, writing to a filename.nnn output file, then read up-to the next line-break and write that, then close the output file, etc. Obviously the last output file just copies to the end of the input file.

Can you help me with the key filesystem related parts: filesize, reading and writing in chunks and reading to a line-break?

I'll be writing this code test-first, so there's no need to give me a complete answer, unless its a one-liner ;-)

Answer 1

linux has a split command

split -l 100000 file.txt

would split into files of equal 100,000 line size

Answer 2

Check out os.stat() for file size and file.readlines([sizehint]). Those two functions should be all you need for the reading part, and hopefully you know how to do the writing :)

Answer 3

As an alternative method, using the logging library:

>>> import logging.handlers
>>> log = logging.getLogger()
>>> fh = logging.handlers.RotatingFileHandler("D://filename.txt", 
     maxBytes=2**20*100, backupCount=100) 
# 100 MB each, up to a maximum of 100 files
>>> log.addHandler(fh)
>>> log.setLevel(logging.INFO)
>>> f = open("D://biglog.txt")
>>> while True:
...     log.info(f.readline().strip())

Your files will appear as follows:

filename.txt (end of file)
filename.txt.1
filename.txt.2
...
filename.txt.10 (start of file)

This is a quick and easy way to make a huge log file match your RotatingFileHandler implementation.