import re
x = ["- dubuque3528 [21/Jun/2019:15:46:", "- - [21/Jun/2019:15:46:"]
for s in x:
m = re.search(r'-\s*(.*?)\s*\[', s)
if m:
print(m.group(1))
aW1wb3J0IHJlCnggPSBbIi0gZHVidXF1ZTM1MjggWzIxL0p1bi8yMDE5OjE1OjQ2OiIsICItIC0gWzIxL0p1bi8yMDE5OjE1OjQ2OiJdCmZvciBzIGluIHg6CgltID0gcmUuc2VhcmNoKHInLVxzKiguKj8pXHMqXFsnLCBzKQoJaWYgbToKCQlwcmludChtLmdyb3VwKDEpKQ==