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Python negative lookahead for aaa:bbb@hostname

EK 365
EK 365 asked
Last Modified: 2016-04-12
Hi, below python regular expression is for getting id/pwd/hostname/port from user input.

Python Re:

Target String:

Could you please explain above bold formatted characters' roles ?
I am not sure why (:?) has parenthesis however :? before "port" parsing does not have one.
I am not sure why (?!\\) was used why do we need negative look-ahead for '\' ? It works without (?!\\) regex.

Regular Expression tool: http://pythex.org/
Code used: https://github.com/pexpect/pexpect/blob/master/examples/hive.py
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