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# Modifying Functions

## modify-argument

> Function modifications consist of a list of `modify-argument` nodes contained in a modify-function node. Use the remove-argument, replace-default-expression, remove-default-expression, replace-type, reference-count and define-ownership nodes to specify the details of the modification.

>     <modify-function>
>         <modify-argument index="return | this | 1 ..." rename="..."
>          invalidate-after-use = "true | false" pyi-type="...">
>             // modifications
>         </modify-argument>
>     </modify-function>

> Set the `index` attribute to “1” for the first argument, “2” for the second one and so on. Alternatively, set it to “return” or “this” if you want to modify the function’s return value or the object the function is called upon, respectively.

> The optional `rename` attribute is used to rename a argument and use this new name in the generated code.

> The optional `pyi-type` attribute specifies the type to appear in the signature strings and `.pyi` files. The type string is determined by checking this attribute value, the replace-type modification and the C++ type. The attribute can be used for example to enclose a pointer return value within `Optional[]` to indicate that `None` can occur.

> For the optional `invalidate-after-use` attribute, see Invalidation after use .