DebugFilesKeyError Class — flask Architecture

Source Code

src/flask/debughelpers.py lines 23–47

class DebugFilesKeyError(KeyError, AssertionError):
    """Raised from request.files during debugging.  The idea is that it can
    provide a better error message than just a generic KeyError/BadRequest.
    """

    def __init__(self, request: Request, key: str) -> None:
        form_matches = request.form.getlist(key)
        buf = [
            f"You tried to access the file {key!r} in the request.files"
            " dictionary but it does not exist. The mimetype for the"
            f" request is {request.mimetype!r} instead of"
            " 'multipart/form-data' which means that no file contents"
            " were transmitted. To fix this error you should provide"
            ' enctype="multipart/form-data" in your form.'
        ]
        if form_matches:
            names = ", ".join(repr(x) for x in form_matches)
            buf.append(
                "\n\nThe browser instead transmitted some file names. "
                f"This was submitted: {names}"
            )
        self.msg = "".join(buf)

    def __str__(self) -> str:
        return self.msg