The caret character ^ anchors a regular expression to the beginning of the input, or (for multi-line regular expressions) to the beginning of a line. If it is preceded by a pattern that must match a non-empty sequence of (non-newline) input characters, then the entire regular expression cannot match anything.

Examine the regular expression to find and correct any typos.

In the following example, the regular expression r"\[^.]*\.css" cannot match any string, since it contains a caret assertion preceded by an escape sequence that matches an opening bracket.

In the second regular expression, r"[^.]*\.css", the caret is part of a character class, and will not match the start of the string.

Python Standard Library: Regular expression operations.

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