Question

I would like to replicate this in python:

gvimdiff <(hg cat file.txt) file.txt 

(hg cat file.txt outputs the most recently committed version of file.txt)

I know how to pipe the file to gvimdiff, but it won’t accept another file:

$ hg cat file.txt | gvimdiff file.txt - Too many edit arguments: '-' 

Getting to the python part…

# hgdiff.py import subprocess import sys file = sys.argv[1] subprocess.call(['gvimdiff', '<(hg cat %s)' % file, file]) 

When subprocess is called it merely passes <(hg cat file) onto gvimdiff as a filename.

So, is there any way to redirect a command as bash does? For simplicity’s sake just cat a file and redirect it to diff:

diff <(cat file.txt) file.txt 

Answer 1

It can be done. As of Python 2.5, however, this mechanism is Linux-specific and not portable:

import subprocess import sys  file = sys.argv[1] p1 = subprocess.Popen(['hg', 'cat', file], stdout=subprocess.PIPE) p2 = subprocess.Popen([     'gvimdiff',     '/proc/self/fd/%s' % p1.stdout.fileno(),     file]) p2.wait() 

That said, in the specific case of diff, you can simply take one of the files from stdin, and remove the need to use the bash-alike functionality in question:

file = sys.argv[1] p1 = subprocess.Popen(['hg', 'cat', file], stdout=subprocess.PIPE) p2 = subprocess.Popen(['diff', '-', file], stdin=p1.stdout) diff_text = p2.communicate()[0]