Paging output from python

Question

I'm trying to implement something similar to git log, which will only page the output if the log is of a certain length. If you're not familiar with git, I'm essentially trying to achieve this:

python some_script.py | less

With some help from the paging implementation in python2.6/pydoc.py, I was able to come up with this:

import os
text = '...some text...'
pipe = os.popen('less', 'w')
pipe.write(text)
pipe.close()

which works great, but os.popen() is deprecated. I've considered writing to a temp file and calling less with its path, but that doesn't seem ideal. Is this possible with subprocess? Any other ideas?

EDIT:

So I've gotten subprocess working. I was able to give it the text variable with Popen.communicate(text), but since I really want to redirect print statements, I've settled on this:

  import os, sys, subprocess, tempfile

  page = True
  if page:
      path = tempfile.mkstemp()[1]
      tmp_file = open(path, 'a')
      sys.stdout = tmp_file
  print '...some text...'
  if page:
      tmp_file.flush()
      tmp_file.close()
      p = subprocess.Popen(['less', path], stdin=subprocess.PIPE)
      p.communicate()
      sys.stdout = sys.__stdout__     

Of course, I'd end up wrapping it into functions. Does anyone see a problem with that?

Answer 1

How about this:

import pydoc
text = '... some text ... '
pydoc.pager(text)

This (on my opensuse linux box) sends the text to a pager ('less' in my case), and works the same as calling "help(... python command...)" within the Python interpreter.

Answer 2

It is a good idea to be explicit in your code, so that it shows that you use a special print function printc() instead of the standard one. Using subprocess.call() is also sufficient (you don't need the pipe machinery). Furthermore, you can save a variable by not storing the name of the temporary file:

from __future__ import print_function

import subprocess, tempfile

page = True  # For tests

# Definition of a printc() function that prints to the correct output
if page:
    tmp_file = open(tempfile.mkstemp()[1], 'w')  # No need to store the name in a specific variable
    def printc(*largs, **kwargs):
        if 'file' not in kwargs:  # The code can still use the usual file argument of print()
            kwargs['file'] = tmp_file  # Forces the output to go to the temp file
        print(*largs, **kwargs)
else:
    printc = print  # Regular print

# Main program:

printc('...some text...', 'some more text', sep='/')  # Python3 syntax

# Paging of the current contents of the temp file:
if page:
    tmp_file.flush()  # No need to close the file: you can keep printing to it
    subprocess.call(['less', tmp_file.name])  # Simpler than a full Popen()

This way, you get the flexibility of Python 3's print function, with a code that explicitly shows that you're doing some fancy printing stuff. This scales better with larger programs than modifying the "global" sys.stdout variable in some locations of your code.

Answer 3

Use subprocess.Popen instead.

http://docs.python.org/library/subprocess.html#subprocess-replacements

http://docs.python.org/library/subprocess.html#subprocess.Popen

There is even a note about this in the os.popen docs.

http://docs.python.org/library/os.html#os.popen

Answer 4

I didn't like executing external commands, so I wrote pager in pure Python. It still has a problem - piped input works only for Windows.