# Creating and Adding SysML elements to Model

**URL:** <https://forum.sensmetry.com/t/creating-and-adding-sysml-elements-to-model/464>\
**Category:** Questions / Help\
**Tags:** automator\
**Created:** [May 5, 2026, 7:53am UTC](https://forum.sensmetry.com/t/creating-and-adding-sysml-elements-to-model/464 "2026-05-05T07:53:18Z")\
**Posts on this page:** 6\
**Page:** 1

<div class="post-metadata">

**Author:** ![TomBaker](https://avatars.discourse-cdn.com/v4/letter/t/e47c2d/32.png) [@TomBaker](https://forum.sensmetry.com/u/TomBaker)\
**Post date:** [May 5, 2026, 7:53am UTC](https://forum.sensmetry.com/t/creating-and-adding-sysml-elements-to-model/464/1 "2026-05-05T07:53:18Z")

</div>

Hello,

Do you have a simple example of how one can programmatically extend the model?

My model currently has part definitions and I would like to add their corresponding requirements to the model:

1. I could generate .sysml files via a template but is there a way to create elements in the model using the SysIDE python API?
2. How do associate the created requirement elements with the existing part definitions in the model?

Thanks!

Tom

---

<div class="post-metadata">

**Author:** ![Daumantas](https://yyz2.discourse-cdn.com/flex008/user_avatar/forum.sensmetry.com/daumantas/32/19_2.png) [@Daumantas](https://forum.sensmetry.com/u/Daumantas)\
**Post date:** [May 5, 2026, 8:24am UTC](https://forum.sensmetry.com/t/creating-and-adding-sysml-elements-to-model/464/2 "2026-05-05T08:24:12Z")

</div>

Hi,

For namespace body elements you would use `.children`, e.g. creating a new owned attribute

```py
membership, attribute = part.children.append(syside.FeatureMembership, syside.AttributeUsage)
# modify `attribute` as needed

```

For references, you would need to pass an existing element

```py
membership, attribute = part.children.append(syside.Membership, attribute)

```

Generally, there are 3 common cases:

- `.append(<owning membership type>, <child type>)` will create empty membership and child elements
- `.append(<owning membership type>, child)` will create an empty membership and take ownership of `child`
- `.append(<relationship type>, element)` will create an empty non-owning `relationship` with a reference to `element`

Relationships are currently only allowed to be constructed automatically as they rarely need to be modified. With dependent generics, this also catches related element type mistmatches statically (sadly, not supported by Python).

cst.syside.app has recently been updated to match field names with the API, e.g.

 ![image](https://canada1.discourse-cdn.com/flex008/uploads/syside/original/1X/8d6374c590604b07075dc22a3d2826090a433d13.jpeg)

(Note general purpose `target` and `source` fields, these will be automatically updated with a given element on construction, e.g. using `.append`).

Common accessors for modifying the model include:

- [NamespaceBody](https://docs.sensmetry.com/python/latest/syside/NamespaceBody.html#syside.NamespaceBody)
- [Heritage](https://docs.sensmetry.com/python/latest/syside/Heritage.html#syside.Heritage)

All mutable accessors are children of [ChildrenNodes](https://docs.sensmetry.com/python/latest/syside/ChildrenNodes.html#syside.ChildrenNodes) (multiple) and [MemberAccessor](https://docs.sensmetry.com/python/latest/syside/MemberAccessor.html#syside.MemberAccessor) (single). See `Used in` at the bottom of each type page for places where they are used.

These are distinct types to improve static type checking and type inference because Python does not support generics of higher-kind.

---

<div class="post-metadata">

**Author:** ![TomBaker](https://avatars.discourse-cdn.com/v4/letter/t/e47c2d/32.png) [@TomBaker](https://forum.sensmetry.com/u/TomBaker)\
**Post date:** [May 12, 2026, 3:46pm UTC](https://forum.sensmetry.com/t/creating-and-adding-sysml-elements-to-model/464/3 "2026-05-12T15:46:07Z")

</div>

Thanks for your reply! I’m trying to apply it to a concrete example, but I’m having some difficulty.

For the following model example I have a python script that extracts the System and myReq elements.

```auto
package Example {
	part def System;
	requirement myReq;
}

```

Now I would like to programmatically modify the model (i.e. the .sysml files) to look like this:

```auto
package Example {
	part def System {
        satisfy myReq;
    }
	requirement myReq;
}

```

What would the python script look like?

Thanks!

---

<div class="post-metadata">

**Author:** ![Daumantas](https://yyz2.discourse-cdn.com/flex008/user_avatar/forum.sensmetry.com/daumantas/32/19_2.png) [@Daumantas](https://forum.sensmetry.com/u/Daumantas)\
**Post date:** [May 13, 2026, 5:56am UTC](https://forum.sensmetry.com/t/creating-and-adding-sysml-elements-to-model/464/4 "2026-05-13T05:56:33Z")

</div>

> [@TomBaker](#):
>
> ```auto
> package Example {
> part def System {
> satisfy myReq;
> }
> requirement myReq;
> }
> 
> ```

You need to replicate the structure as it would appear in text, e.g.

```py
_, satisfy = system.children.append(syside.FeatureMembership, syside.SatisfyRequirementUsage)
_ = satisfy.heritage.append(sysisde.ReferenceSubsetting, my_req)

```

 ![image](https://canada1.discourse-cdn.com/flex008/uploads/syside/original/1X/085cd30fb2ba2b1c73fa569ff255464cc41a2314.jpeg)

---

<div class="post-metadata">

**Author:** ![TomBaker](https://avatars.discourse-cdn.com/v4/letter/t/e47c2d/32.png) [@TomBaker](https://forum.sensmetry.com/u/TomBaker)\
**Post date:** [May 13, 2026, 2:07pm UTC](https://forum.sensmetry.com/t/creating-and-adding-sysml-elements-to-model/464/5 "2026-05-13T14:07:59Z")

</div>

Thank you! I think I understand the steps now!

I was also missing the steps before and after, but I found some useful snippets in the examples. Here’s my working example:

```python
import syside

def get_element_by_type(model: syside.Model, type: str) -> list[syside.Element]:
    """Return a list of elements from the model that have the given type (e.g. "AttributeUsage", "PartDefinition", etc.)."""
    
    elements = []
    for element in model.elements(syside.Element, include_subtypes=True):
        if element.cst_node is not None:
            if element.cst_node.type == type:
                elements.append(element)
    
    return elements

SRC = """\
package ExtendModelExample {
	part def System;
	requirement myReq;
}
"""

# Load model
model, _ = syside.load_model(sysml_source=SRC)
model_document = model.user_docs[0]

with model_document.lock() as doc:
    root = doc.root_node

    # Get elements from model
    part_defs = get_element_by_type(model, "PartDefinition")
    system = part_defs[0]
    req_usages = get_element_by_type(model, "RequirementUsage")
    my_req = req_usages[0]
    
    # Add satisfy relationship
    _, satisfy = system.children.append(syside.FeatureMembership, syside.SatisfyRequirementUsage)
    _ = satisfy.heritage.append(syside.ReferenceSubsetting, my_req)

    # Update model
    printer_cfg = syside.PrinterConfig(line_width=80, tab_width=4)
    printer = syside.ModelPrinter.sysml()
    sysml_text = syside.pprint(root, printer, printer_cfg)

    with open("ExtendModelExample.sysml", "w", encoding="utf-8") as fp:
        fp.write(sysml_text)

```

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<div class="post-metadata">

**Author:** ![Daumantas](https://yyz2.discourse-cdn.com/flex008/user_avatar/forum.sensmetry.com/daumantas/32/19_2.png) [@Daumantas](https://forum.sensmetry.com/u/Daumantas)\
**Post date:** [May 13, 2026, 2:22pm UTC](https://forum.sensmetry.com/t/creating-and-adding-sysml-elements-to-model/464/6 "2026-05-13T14:22:54Z")

</div>

`get_element_by_type` can be improved

```py
def get_element_by_type[T: syside.Element](model: syside.Model, type: type[T]) -> list[T]:
    return list(model.elements(type, include_subtypes=True)

```

This is both more concise and propagates the element types to the type system for IDE support, e.g. auto-completion.