import re
f = """First line.
2. Second line
03 Third line
04. Fourth line
5. Line.
6 Line""".splitlines()
#with open("file.txt") as f:
for line in f:
print(re.sub("^[0-9]+\.?\s*", "", line))
aW1wb3J0IHJlCmYgPSAiIiJGaXJzdCBsaW5lLgoyLiBTZWNvbmQgbGluZSAKMDMgVGhpcmQgbGluZQowNC4gRm91cnRoIGxpbmUKNS4gTGluZS4gCjYgTGluZSIiIi5zcGxpdGxpbmVzKCkKI3dpdGggb3BlbigiZmlsZS50eHQiKSBhcyBmOgpmb3IgbGluZSBpbiBmOgoJcHJpbnQocmUuc3ViKCJeWzAtOV0rXC4/XHMqIiwgIiIsIGxpbmUpKQ==