# Deep spell override paths

**🟠 Advanced · Lesson 01**

Deep override - the ">"-path form. A path of parameter names walks the dependency graph from the melded root and REPLACES the actual object at that socket: override={"transport>credentials": my_object} Untargeted sockets keep their DI-resolved defaults WITHIN the call; a path that matches nothing refuses. But read the second half of this lesson before you reach for it: under a singleton lifetime the overridden meld BUILDS the singleton, so the substitution outlives the call that made it. This is the surgical form - injecting a fixture or a variant into the MIDDLE of a real graph at meld time without rebinding anything. The simple top-level form (flat dict into the root's own constructor) is intermediate lesson 08.

## Before you run

Use the [Advanced guide](../../advanced/index.md) for prerequisite concepts. Run from a checkout with Melder installed and Python 3.14 free-threading selected. The collection download includes the level's local helper modules.

## Run the saved script

```bash
python UX_and_AIX_experiences/03_advanced/01_deep_spell_override_paths.py
```

```powershell
py -3.14t UX_and_AIX_experiences/03_advanced/01_deep_spell_override_paths.py
```

{download}`Download this collection <../../downloads/advanced-examples.zip>` · [Source on GitHub](https://github.com/Synaptic724/melder/blob/0895ce795453cd87e35d70665957b4e89aad3317/UX_and_AIX_experiences/03_advanced/01_deep_spell_override_paths.py)

## Public surface

meld(override={"path>to>socket": object})

## Code

```{literalinclude} ../../downloads/03_advanced/01_deep_spell_override_paths.py
:language: python
:linenos:
```

## Check the outcome

The script contains its own assertions or demonstrated refusal paths. Run it to evaluate those checks against your installed version. The code above is taken directly from the saved file; no run output is invented here.

[More advanced examples](index.md) · [Level guide](../../advanced/index.md)

## Related guides

- [Deep, wildcard, and broadcast overrides](../../advanced/overrides.md)