docs: add common pitfalls section to deploying custom code

docs/custom_code.qmd

@@ -2,12 +2,12 @@
 
 In some cases, you may need to create and deploy custom code as part of your MLOps workflow using vetiver. This could be necessary when you need to:
 
-- deploy custom models in vetiver
-- deploy unsupported models in vetiver
-- include custom code in vetiver
-- deploy a vetiver model with a custom pipeline
+-   deploy custom models in vetiver
+-   deploy unsupported models in vetiver
+-   include custom code in vetiver
+-   deploy a vetiver model with a custom pipeline
 
- You may also have custom code in a known framework, such as a column transformer for a scikit-learn model.
+You may also have custom code in a known framework, such as a column transformer for a scikit-learn model.
 
 In these cases, extra steps will be required to successfully create and deploy a `VetiverModel` object.
 
@@ -17,12 +17,12 @@ Vetiver supports basic [scikit-learn](https://scikit-learn.org/), [torch](https:
 
 To create a model handler, you should create a subclass of vetiver's `BaseHandler` class. This handler should include the following:
 
-- `model_type`:  A static method that declares the type of your model.
-- `handler_predict()`: A method that defines how predictions should be made for your model. This method is used at the /predict endpoint in the VetiverAPI.
+-   `model_type`: A static method that declares the type of your model.
+-   `handler_predict()`: A method that defines how predictions should be made for your model. This method is used at the /predict endpoint in the VetiverAPI.
 
 Here's an example of a handler for a model of `newmodeltype` type. Once you have defined your handler, you can initialize it with your model and pass it to the `VetiverModel` class.
 
-```python
+``` python
 from vetiver.handlers.base import BaseHandler
 
 class CustomHandler(BaseHandler):
@@ -60,7 +60,7 @@ To deploy custom code, you need to include the necessary source code in your dep
 
 If your `VetiverModel` includes custom source code, you need to include that code in your deployment files to build an API in another location. The example below shows a user-created `FeatureSelector`, which is part of a scikit-learn pipeline.
 
-```{.python filename="model.py"}
+``` {.python filename="model.py"}
 from sklearn.base import BaseEstimator, TransformerMixin
 from sklearn.tree import DecisionTreeClassifier
 from sklearn.pipeline import Pipeline
@@ -94,18 +94,18 @@ board = pins.board_connect(allow_pickle_read=True)
 vetiver_pin_write(board, v)
 ```
 
-::: {.panel-tabset}
+::: panel-tabset
 ## Docker
 
 To generate files needed to start a Docker container, you can use the command `vetiver.prepare_docker`.
 
-```{.python}
+``` python
 vetiver.prepare_docker(board, "selected_decision_tree")
 ```
 
 When you run this line, 3 files are generated: a Dockerfile, an `app.py` file, and a `vetiver_requirements.txt`. In the `app.py` file, you'll need to add an import statement that is formatted `from {name of file, excluding .py, that has custom element} import {name of custom element}`.
 
-```{.python filename="app.py"}
+``` {.python filename="app.py"}
 from vetiver import VetiverModel
 import vetiver
 import pins
@@ -121,7 +121,7 @@ api = vetiver_api.app
 
 Add a line to your Dockerfile to copy your source file(s) into your Docker container. The format will be `COPY path/to/your/filename.py /vetiver/app/filename.py`, where the destination is always in the `/vetiver/app/` directory.
 
-```{.bash filename="Dockerfile"}
+``` {.bash filename="Dockerfile"}
 # # Generated by the vetiver package; edit with care
 # start with python base image
 FROM python:3.10
@@ -152,13 +152,13 @@ CMD ["uvicorn", "app.app:api", "--host", "0.0.0.0", "--port", "8080"]
 
 To deploy custom code to Posit Connect, you'll first start with the command `vetiver.write_app`.
 
-```{.python}
+``` python
 vetiver.write_app(board, 'selected_decision_tree')
 ```
 
 This will generate an `app.py` file, where you'll need to add an import statement that is formatted `from {name of file, excluding .py, that has custom element} import {name of custom element}`.
 
-```{.python filename=="app.py"}
+``` {.python filename="=\"app.py\""}
 from vetiver import VetiverModel
 import vetiver
 import pins
@@ -174,7 +174,7 @@ api = vetiver_api.app
 
 After editing the `app.py` file, you can deploy it to Posit Connect using the `rsconnect` package. Use the `rsconnect.api.actions.deploy_python_fastapi()` function to deploy the API, specifying the Connect server URL, API key, directory containing the `app.py` and `model.py` files, and the entry point of the API.
 
-```{.python}
+``` python
 from rsconnect.api.actions import deploy_python_fastapi
 import rsconnect
 
@@ -191,9 +191,15 @@ rsconnect.actions.deploy_python_fastapi(
         directory = "./", # path to the directory containing the app.py and model.py files
         entry_point = "app:api" # the API is the app.py file, in a variable named api
     )
-
 ```
-
 :::
 
+## Common Pitfalls
+
+When deploying custom code, the most common error is something similar to `AttributeError: Can't get attribute 'ExampleModel' on <module '__main__' (built-in)>`. There are a few possible causes for this error:
+
+1.  The original `ExampleModel` may have been pinned from inside a Jupyter Notebook. Because pickling only saves a reference for how to read a class, not the source code, a custom model transformer pinned from a Jupyter Notebook cannot be imported and resolved later. To fix this, repin your model/transformer from inside a Python script.
+
+2.  You may not be uploading the custom code to be used later. When deploying, you'll want to add the files containing your custom code to the `extra_files` argument so that it can be imported, eg, `vetiver.deploy_rsconnect(connect_server, board, model_name, extra_files=['custom_model.py', 'requirements.txt'])` .
+
 Please note that the above steps are a general guide, and you may need to adapt them to your specific use case and deployment environment. If you have any questions, please consider [opening an issue](https://github.com/rstudio/vetiver-python/issues/new).