import re
regex = re.compile(r"(^[^|\n]*\|)?[^|\n](?=[^|\n]*\|)", flags=re.MULTILINE)
test_str = ("++++|+++This|Is|An|Example++|++++\n\n"
"+\n"
"+|+\n"
"+|+|+\n")
subst = "$1a"
result = regex.sub(subst, test_str)
if result:
print(result)
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