Unmatchable caret in regular expression¶
ID: py/regex/unmatchable-caret Kind: problem Security severity: Severity: error Precision: high Tags: - quality - reliability - correctness Query suites: - python-code-quality.qls - python-security-and-quality.qls Click to see the query in the CodeQL repository
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.
Recommendation¶
Examine the regular expression to find and correct any typos.
Example¶
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.
import re #Regular expression includes a caret, but not at the start. matcher = re.compile(r"\[^.]*\.css") def find_css(filename): if matcher.match(filename): print("Found it!") #Regular expression for a css file name fixed_matcher_css = re.compile(r"[^.]*\.css") References¶
Python Standard Library: Regular expression operations.
Regular-Expressions.info: Start of String and End of String Anchors.