LGTM.com - false positive - unmatchable dollar in regular expression

[DrGFreeman]

Description of the false positive

"Unmatchable dollar in regular expression" is raised against the following regex in Python:

r'((25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)(\.|$)){4}$'

This regex is for an IP address and works properly.

The documentation for Unmatchable dollar in regular expression states

Regular expressions containing a dollar '$' in the middle cannot be matched, whatever the input.

This is not the case in the above regex where the middle '$' is matched at the end of the fourth digits group.

URL to the alert on the project page on LGTM.com

https://lgtm.com/projects/g/freedomofpress/securedrop/snapshot/59b396e032e91e91e51fd76d6980ad1af5b17c43/files/admin/securedrop_admin/__init__.py?sort=name&dir=ASC&mode=heatmap#x651bb88f983a131:1