pytest-dev/pytest · error · ValueError

line not found in output

Error message

line {fnline!r} not found in output

What it means

Thrown by LineMatcher.get_lines_after() when no line in the captured output exactly equals or fnmatches the requested fnline. It returns lines following a match; no match means no anchor was found.

Solutions

1. Print the captured lines (print('\n'.join(matcher.lines))) to see what's actually there.
2. Use a glob pattern with wildcards if the line has variable content.
3. Confirm the marker is written to the same stream the LineMatcher is reading.

Example fix

// before
after = result.stdout.get_lines_after("== RESULTS ==")
// after
print('\n'.join(result.stdout.lines))
after = result.stdout.get_lines_after("*RESULTS*")

lines = result.stdout.lines
if not any(fnline == l or fnmatch(l, fnline) for l in lines):
    pytest.fail(f'anchor {fnline!r} not in output:\n' + '\n'.join(lines))
after = result.stdout.get_lines_after(fnline)

When it happens

Trigger: Calling result.stdout.get_lines_after('some marker') where 'some marker' never appears in the captured output; whitespace/encoding differences between expected and actual lines; glob pattern that doesn't match any line.

Common situations: Asserting on output structure where the anchor line was conditional and didn't print; trailing whitespace stripping differences; OS-specific line endings; output redirected such that the marker went to a different stream.

Related errors

• could not find test report matching
• ext must not be None
• invalid type for lines2
• pytester.makefile expects a file extension, try .
• absolute tolerance can't be negative

AI-assisted analysis of pytest-dev/pytest@0d6fbdeffa (2026-08-11). Data as JSON: /api/errors/a29daba0c7e7795a. Report an issue: GitHub.

Appendix: source

Thrown at src/_pytest/pytester.py:1634

        for line in lines2:
            for x in self.lines:
                if line == x or match_func(x, line):
                    self._log("matched: ", repr(line))
                    break
            else:
                msg = f"line {line!r} not found in output"
                self._log(msg)
                self._fail(msg)

    def get_lines_after(self, fnline: str) -> Sequence[str]:
        """Return all lines following the given line in the text.

        The given line can contain glob wildcards.
        """
        for i, line in enumerate(self.lines):
            if fnline == line or fnmatch(line, fnline):
                return self.lines[i + 1 :]
        raise ValueError(f"line {fnline!r} not found in output")

    def _log(self, *args) -> None:
        self._log_output.append(" ".join(str(x) for x in args))

    @property
    def _log_text(self) -> str:
        return "\n".join(self._log_output)

    def fnmatch_lines(
        self, lines2: Sequence[str], *, consecutive: bool = False
    ) -> None:
        """Check lines exist in the output (using :func:`python:fnmatch.fnmatch`).

        The argument is a list of lines which have to match and can use glob
        wildcards.  If they do not match a pytest.fail() is called.  The
        matches and non-matches are also shown as part of the error message.

        :param lines2: String patterns to match.

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