# Using classes from a Python plugin in another Python plugin

**URL:** <https://forum.opentap.io/t/using-classes-from-a-python-plugin-in-another-python-plugin/669>\
**Category:** Technical\
**Tags:** python\
**Created:** [April 28, 2022, 2:42pm UTC](https://forum.opentap.io/t/using-classes-from-a-python-plugin-in-another-python-plugin/669 "2022-04-28T14:42:28Z")\
**Posts on this page:** 7\
**Page:** 1

<div class="post-metadata">

**Author:** ![tatiana.boye](https://avatars.discourse-cdn.com/v4/letter/t/ba8739/32.png) [@tatiana.boye](https://forum.opentap.io/u/tatiana.boye)\
**Post date:** [April 28, 2022, 2:42pm UTC](https://forum.opentap.io/t/using-classes-from-a-python-plugin-in-another-python-plugin/669/1 "2022-04-28T14:42:28Z")

</div>

I’m implementing support for some measurement equipment in OpenTAP and I’d like to have the following structure:

- **MyBasePlugin** that contains `MyBaseInstrument` class and a test step that accepts instruments of `MyBaseInstrument` type
- **MyPlugin1** that contains`MyInstrument1` class derived from `MyBaseInstrument`
- **MyPlugin2** that contains`MyInstrument2` class derived from `MyBaseInstrument`

That works fine in case all classes are located in the same plugin, but if I try to do it as described above, I’m facing some issues. They can be reproduced using PluginExample:

```csharp
clr.AddReference("Python.PluginExample")

import Python.PluginExample as PluginExample
BasicInstrument = PluginExample.BasicInstrument

@Attribute(BrowsableAttribute, True)
class MyInstrument1(BasicInstrument):
    pass

```

Building causes the following error:

```csharp
The type or namespace name 'BasicInstrument' does not exist in the namespace 'Python' (are you missing an assembly reference?)
'MyInstrument1.load_instance()': no suitable method found to override
The name 'load' does not exist in the current context
'MyInstrument1' does not contain a definition for 'getValue' and the best extension method overload 'PythonWrapperExtensions.getValue(IPythonWrapper, string, Type)' requires a receiver of type 'IPythonWrapper'
'MyInstrument1' does not contain a definition for 'setValue' and the best extension method overload 'PythonWrapperExtensions.setValue(IPythonWrapper, string, object)' requires a receiver of type 'IPythonWrapper'
'MyInstrument1' does not contain a definition for 'getValue' and the best extension method overload 'PythonWrapperExtensions.getValue(IPythonWrapper, string, Type)' requires a receiver of type 'IPythonWrapper'
'MyInstrument1' does not contain a definition for 'setValue' and the best extension method overload 'PythonWrapperExtensions.setValue(IPythonWrapper, string, object)' requires a receiver of type 'IPythonWrapper'
'MyInstrument1' does not contain a definition for 'Call' and the best extension method overload 'PythonWrapperExtensions.Call<double>(IPythonWrapper, string, params object[])' requires a receiver of type 'IPythonWrapper'

```

Just as an experiment, if I do `BasicInstrument = TapPlugin(PluginExample.BasicInstrument)` instead, it builds successfully and `MyInstrument1` can be added in the Editor. Although it shows some errors and the properties of `BasicInstrument` are of course gone.

Is there a way to do what I’m trying to do?

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<div class="post-metadata">

**Author:** ![tatiana.boye](https://avatars.discourse-cdn.com/v4/letter/t/ba8739/32.png) [@tatiana.boye](https://forum.opentap.io/u/tatiana.boye)\
**Post date:** [April 29, 2022, 9:17am UTC](https://forum.opentap.io/t/using-classes-from-a-python-plugin-in-another-python-plugin/669/2 "2022-04-29T09:17:30Z")

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Update: probably the proper way to import `BasicInstrument` is `from Python.PluginExample.BasicInstrument import BasicInstrument` (i.e. including the namespace), though it doesn’t seem to resolve the issue.

Any input is highly appreciated.

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<div class="post-metadata">

**Author:** ![rolf\_madsen](https://avatars.discourse-cdn.com/v4/letter/r/43a26b/32.png) [@rolf\_madsen](https://forum.opentap.io/u/rolf_madsen)\
**Post date:** [May 2, 2022, 8:07am UTC](https://forum.opentap.io/t/using-classes-from-a-python-plugin-in-another-python-plugin/669/3 "2022-05-02T08:07:36Z")

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In this version of the python plugin, the BasicInstrument class has two implementations, one C# implementation which is what you are currently using and one python implementation.  
I believe you should be able to import PluginExample and use PluginExample.BasicInstrument (the python implementation), _not_ Python.PluginExample.BasicInstrument, which is the C# class.

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<div class="post-metadata">

**Author:** ![tatiana.boye](https://avatars.discourse-cdn.com/v4/letter/t/ba8739/32.png) [@tatiana.boye](https://forum.opentap.io/u/tatiana.boye)\
**Post date:** [May 2, 2022, 9:27am UTC](https://forum.opentap.io/t/using-classes-from-a-python-plugin-in-another-python-plugin/669/4 "2022-05-02T09:27:51Z")

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@rolf_madsen Thanks for the input. I can import directly from Python indeed, but it will be a different class therefore all inheritance will be lost.

Editor will load `Python.PluginExample.BasicInstrument` whereas my implementation will derive from `PluginExample.BasicInstrument` so these two instruments won’t be interchangeable.

Could you give me some insights on why it’s not possible to import from DLL built in OpenTAP? Is it a known limitation?

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<div class="post-metadata">

**Author:** ![rolf\_madsen](https://avatars.discourse-cdn.com/v4/letter/r/43a26b/32.png) [@rolf\_madsen](https://forum.opentap.io/u/rolf_madsen)\
**Post date:** [May 2, 2022, 10:29am UTC](https://forum.opentap.io/t/using-classes-from-a-python-plugin-in-another-python-plugin/669/5 "2022-05-02T10:29:43Z")

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What do you mean that inheritance will be lost?

I think that you are right that these two class might not alias to eachother, but you might be able to use interfaces to get around that. Anyway, you are saying that if you have a test ste[ that has a PlugnExample.BasicInstrument property and an instrument which is a MyPlugin.BasicInstrument2, it cannot be assigned there?

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<div class="post-metadata">

**Author:** ![tatiana.boye](https://avatars.discourse-cdn.com/v4/letter/t/ba8739/32.png) [@tatiana.boye](https://forum.opentap.io/u/tatiana.boye)\
**Post date:** [May 2, 2022, 10:49am UTC](https://forum.opentap.io/t/using-classes-from-a-python-plugin-in-another-python-plugin/669/6 "2022-05-02T10:49:31Z")

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If the test step is located in `PluginExample` it will expect `Python.PluginExample.BasicInstrument` so it won’t be possible to use `MyPlugin1.BasicInstrument` as it derives from a different class, namely `PluginExample.BasicInstrument`.

If the test step is located in MyPlugin1, it will accept `MyPlugin1.BasicInstrument` but won’t accept `Python.PluginExample.BasicInstrument` that will be loaded from `PluginExample`.

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<div class="post-metadata">

**Author:** ![rolf\_madsen](https://avatars.discourse-cdn.com/v4/letter/r/43a26b/32.png) [@rolf\_madsen](https://forum.opentap.io/u/rolf_madsen)\
**Post date:** [May 2, 2022, 7:08pm UTC](https://forum.opentap.io/t/using-classes-from-a-python-plugin-in-another-python-plugin/669/7 "2022-05-02T19:08:46Z")

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Ok, I thought we supported that., but maybe only within one python module.

Anyway, again I am happy to say that this is fixed in 3.0, so its getting fixed. 🙂