def tolerance(self):
        """Return the tolerance for the comparison.

        This could be either an absolute tolerance or a relative tolerance,
        depending on what the user specified or which would be larger.
        """

        def set_default(x, default):
            return x if x is not None else default

        # Figure out what the absolute tolerance should be.  ``self.abs`` is
        # either None or a value specified by the user.
        absolute_tolerance = set_default(self.abs, self.DEFAULT_ABSOLUTE_TOLERANCE)

        if absolute_tolerance < 0:
            raise ValueError(
                f"absolute tolerance can't be negative: {absolute_tolerance}"
            )
        if math.isnan(absolute_tolerance):
            raise ValueError("absolute tolerance can't be NaN.")

        # If the user specified an absolute tolerance but not a relative one,
        # just return the absolute tolerance.
        if self.rel is None:
            if self.abs is not None:
                return absolute_tolerance

        # Figure out what the relative tolerance should be.  ``self.rel`` is
        # either None or a value specified by the user.  This is done after
        # we've made sure the user didn't ask for an absolute tolerance only,
        # because we don't want to raise errors about the relative tolerance if
        # we aren't even going to use it.
        relative_tolerance = set_default(
            self.rel, self.DEFAULT_RELATIVE_TOLERANCE
        ) * abs(self.expected)

        if relative_tolerance < 0:
            raise ValueError(
                f"relative tolerance can't be negative: {relative_tolerance}"
            )
        if math.isnan(relative_tolerance):
            raise ValueError("relative tolerance can't be NaN.")

        # Return the larger of the relative and absolute tolerances.
        return max(relative_tolerance, absolute_tolerance)
Return the tolerance for the comparison.

        This could be either an absolute tolerance or a relative tolerance,
        depending on what the user specified or which would be larger.
        
src/_pytest/python_api.py