Question

I am currently reproducing the following Unix command:

cat command.info fort.13 > command.fort.13

in Python with the following:

with open('command.fort.13', 'w') as outFile:
  with open('fort.13', 'r') as fort13, open('command.info', 'r') as com:
    for line in com.read().split('\n'):
      if line.strip() != '':
        print >>outFile, line
    for line in fort13.read().split('\n'):
      if line.strip() != '':
        print >>outFile, line

which works, but there has to be a better way. Any suggestions?

Edit (2016):

This question has started getting attention again after four years. I wrote up some thoughts in a longer Jupyter Notebook here.

The crux of the issue is that my question was pertaining to the (unexpected by me) behavior of readlines. The answer I was aiming toward could have been better asked, and that question would have been better answered with read().splitlines().

Answer 1

The easiest way might be simply to forget about the lines, and just read in the entire file, then write it to the output:

with open('command.fort.13', 'wb') as outFile:
    with open('command.info', 'rb') as com, open('fort.13', 'rb') as fort13:
        outFile.write(com.read())
        outFile.write(fort13.read())

As pointed out in a comment, this can cause high memory usage if either of the inputs is large (as it copies the entire file into memory first). If this might be an issue, the following will work just as well (by copying the input files in chunks):

import shutil
with open('command.fort.13', 'wb') as outFile:
    with open('command.info', 'rb') as com, open('fort.13', 'rb') as fort13:
        shutil.copyfileobj(com, outFile)
        shutil.copyfileobj(fort13, outFile)