# coding=utf8
# the above tag defines encoding for this document and is for Python 2.x compatibility
import re
regex = r"(a)?b(?(1)c|d)"
test_str = ("matches bd and abc. It does not match bc, but does match bd in abd. Let's see how this regular expression works on each of these four subject strings.\n"
"If-Then-Else Conditionals in Regular Expressions\n"
"http://www.regular-expressions.info/conditional.html")
subst = "\\1"
# You can manually specify the number of replacements by changing the 4th argument
result = re.sub(regex, subst, test_str, 0, re.MULTILINE)
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