Script to remove line-breaks from plain text paragraphs

#! /usr/bin/env python

"""\
%prog <infile>

Remove line breaks from block paragraphs of plain text, but retain multiple
consecutive newlines used for e.g. LaTeX, MarkDown, or plain text formats.

TODO:
 * Provide a -o flag to write out to file
 * Read in from stdin if no files provided
"""

import optparse
op = optparse.OptionParser(usage=__doc__)
opts, args = op.parse_args()

lines = None
infile = args[0]
with open(infile, "r") as f:
    lines = f.readlines()

newtext = ""
inpara = False
for l in lines:
    l2 = l.rstrip() # lose newline and trailing whitespace
    if not inpara:
        if l2:
            newtext += l2
            inpara = True
        else:
            newtext += l
        continue
    else: # in para
        if l2:
            newtext += " " + l2.lstrip()
        else:
            newtext += "\n" + l
            inpara = False

print newtext