# coding=utf8
# the above tag defines encoding for this document and is for Python 2.x compatibility
import re
regex = r"(\\index\{(\w+(?:\s+\w+){0,4})\})"
test_str = ("blah blah \\index{words}words ramble on\n"
"more blah more blah\\index{space words} space words ramble on\n"
"final blah\\textbf{bold words} ramble on\n"
"final blah\\index{word1 word2 word3 word4 word5 word6} ramble on")
subst = "\\1\\\\textbf{\\2}"
# You can manually specify the number of replacements by changing the 4th argument
result = re.sub(regex, subst, test_str, 0)
if result:
print (result)
# Note: for Python 2.7 compatibility, use ur"" to prefix the regex and u"" to prefix the test string and substitution.
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for Python, please visit: https://docs.python.org/3/library/re.html