# How to add or edit a derived tag in script?

**URL:** <https://forum.inductiveautomation.com/t/how-to-add-or-edit-a-derived-tag-in-script/30347>\
**Category:** Ignition\
**Tags:** ignition79\
**Created:** [December 2, 2019, 3:48am UTC](https://forum.inductiveautomation.com/t/how-to-add-or-edit-a-derived-tag-in-script/30347 "2019-12-02T03:48:20Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![guanghui](https://avatars.discourse-cdn.com/v4/letter/g/43a26b/32.png) [@guanghui](https://forum.inductiveautomation.com/u/guanghui)\
**Post date:** [December 2, 2019, 3:48am UTC](https://forum.inductiveautomation.com/t/how-to-add-or-edit-a-derived-tag-in-script/30347/1 "2019-12-02T03:48:20Z")

</div>

I want to add a derived tag using python , but I have no idea how to set the Read Expression value.  
is it possiable just like below or something else?  
system.tag.addTag(parentPath=’[default]test’, name=“tag\_43”, tagType=“DERIVED”, dataType=“Float4”, attributes={“SourceTagPath”:"[default]coderise/10001",“ValueDerivation”:{“ReadExpression”:"{Source}\*2"}})  
 ![image](https://us1.discourse-cdn.com/inductiveautomation/original/2X/2/2bf5eda2dcb8c8c78d41d4186ee06b2fd76ea8fa.png)