Method process_value

src/click/core.py:2536–2600

Process the value of this parameter: 1. Type cast the value using :meth:`type_cast_value`. 2. Check if the value is missing (see: :meth:`value_is_missing`), and raise :exc:`MissingParameter` if it is required. 3. If a :attr:`callback` is set, call it to have the v

(self, ctx: Context, value: t.Any)

        return False

    def process_value(self, ctx: Context, value: t.Any) -> t.Any:
        """Process the value of this parameter:

        1. Type cast the value using :meth:`type_cast_value`.
        2. Check if the value is missing (see: :meth:`value_is_missing`), and raise
           :exc:`MissingParameter` if it is required.
        3. If a :attr:`callback` is set, call it to have the value replaced by the
           result of the callback. If the value was not set, the callback receive
           ``None``. This keep the legacy behavior as it was before the introduction of
           the :attr:`UNSET` sentinel.

        :meta private:
        """
        # shelter `type_cast_value` from ever seeing an `UNSET` value by handling the
        # cases in which `UNSET` gets special treatment explicitly at this layer
        #
        # Refs:
        # https://github.com/pallets/click/issues/3069
        if value is UNSET:
            if self.multiple or self.nargs == -1:
                value = ()
        else:
            value = self.type_cast_value(ctx, value)

        if self.required and self.value_is_missing(value):
            raise MissingParameter(ctx=ctx, param=self)

        if self.callback is not None:
            # Legacy case: UNSET is not exposed directly to the callback, but converted
            # to None.
            if value is UNSET:
                value = None

            # Search for parameters with UNSET values in the context.
            unset_keys = {k: None for k, v in ctx.params.items() if v is UNSET}
            # No UNSET values, call the callback as usual.
            if not unset_keys:
                value = self.callback(ctx, self, value)

            # Legacy case: provide a temporarily manipulated context to the callback
            # to hide UNSET values as None.
            #
            # Refs:
            # https://github.com/pallets/click/issues/3136
            # https://github.com/pallets/click/pull/3137
            else:
                # Add another layer to the context stack to clearly hint that the
                # context is temporarily modified.
                with ctx:
                    # Update the context parameters to replace UNSET with None.
                    ctx.params.update(unset_keys)
                    # Feed these fake context parameters to the callback.
                    value = self.callback(ctx, self, value)
                    # Restore the UNSET values in the context parameters.
                    ctx.params.update(
                        {
                            k: UNSET
                            for k in unset_keys