A dollar assertion $ in a regular expression only matches at the end of the input, or (for multi-line regular expressions) at the end of a line. If it is followed by a pattern that must match a non-empty sequence of (non-newline) input characters, it cannot possibly match, rendering the entire regular expression unmatchable.

Examine the regular expression to find and correct any typos.

In the following example, the regular expression r"\.$\w+$$" cannot match any string, since it contains a dollar assertion followed by an escape sequence that matches a closing parenthesis.

The second regular expression, r"\.$\w+$$", has the dollar at the end and will work as expected.

Python Standard Library: Regular expression operations.

Regular-Expressions.info: Start of String and End of String Anchors.