Passing None an aes color mapping value raises error

[machow]

plotnine's color aesthetic accepts NA-like values. In this case, NAs are colored grey, and sometimes there are special scale arguments to change the color of NA values, etc..

However, if a None is passed directly to aes, it raises an error:

# Works ----
# could also replace pd.Series(...) with np.nan, pd.NA, etc..
(
    ggplot(mpg2, aes("displ", "hwy", color=pd.Series([None])))
    + geom_point()
)

# Raises error ----
(
    ggplot(mpg2, aes("displ", "hwy", color=None))
    + geom_point()
)

Error:

File [~/.virtualenvs/plotnine-guide/lib/python3.9/site-packages/plotnine/layer.py:463](https://file+.vscode-resource.vscode-cdn.net/Users/machow/repos/plotnine-guide/~/.virtualenvs/plotnine-guide/lib/python3.9/site-packages/plotnine/layer.py:463), in Layers.compute_aesthetics(self, plot)
    [461](https://file+.vscode-resource.vscode-cdn.net/Users/machow/repos/plotnine-guide/~/.virtualenvs/plotnine-guide/lib/python3.9/site-packages/plotnine/layer.py:461) def compute_aesthetics(self, plot: ggplot):
    [462](https://file+.vscode-resource.vscode-cdn.net/Users/machow/repos/plotnine-guide/~/.virtualenvs/plotnine-guide/lib/python3.9/site-packages/plotnine/layer.py:462)     for l in self:
--> [463](https://file+.vscode-resource.vscode-cdn.net/Users/machow/repos/plotnine-guide/~/.virtualenvs/plotnine-guide/lib/python3.9/site-packages/plotnine/layer.py:463)         l.compute_aesthetics(plot)

File [~/.virtualenvs/plotnine-guide/lib/python3.9/site-packages/plotnine/layer.py:260](https://file+.vscode-resource.vscode-cdn.net/Users/machow/repos/plotnine-guide/~/.virtualenvs/plotnine-guide/lib/python3.9/site-packages/plotnine/layer.py:260), in layer.compute_aesthetics(self, plot)
    [253](https://file+.vscode-resource.vscode-cdn.net/Users/machow/repos/plotnine-guide/~/.virtualenvs/plotnine-guide/lib/python3.9/site-packages/plotnine/layer.py:253) def compute_aesthetics(self, plot: ggplot):
    [254](https://file+.vscode-resource.vscode-cdn.net/Users/machow/repos/plotnine-guide/~/.virtualenvs/plotnine-guide/lib/python3.9/site-packages/plotnine/layer.py:254)     """
    [255](https://file+.vscode-resource.vscode-cdn.net/Users/machow/repos/plotnine-guide/~/.virtualenvs/plotnine-guide/lib/python3.9/site-packages/plotnine/layer.py:255)     Return a dataframe where the columns match the aesthetic mappings
    [256](https://file+.vscode-resource.vscode-cdn.net/Users/machow/repos/plotnine-guide/~/.virtualenvs/plotnine-guide/lib/python3.9/site-packages/plotnine/layer.py:256) 
    [257](https://file+.vscode-resource.vscode-cdn.net/Users/machow/repos/plotnine-guide/~/.virtualenvs/plotnine-guide/lib/python3.9/site-packages/plotnine/layer.py:257)     Transformations like 'factor(cyl)' and other
    [258](https://file+.vscode-resource.vscode-cdn.net/Users/machow/repos/plotnine-guide/~/.virtualenvs/plotnine-guide/lib/python3.9/site-packages/plotnine/layer.py:258)     expression evaluation are  made in here
    [259](https://file+.vscode-resource.vscode-cdn.net/Users/machow/repos/plotnine-guide/~/.virtualenvs/plotnine-guide/lib/python3.9/site-packages/plotnine/layer.py:259)     """
--> [260](https://file+.vscode-resource.vscode-cdn.net/Users/machow/repos/plotnine-guide/~/.virtualenvs/plotnine-guide/lib/python3.9/site-packages/plotnine/layer.py:260)     evaled = evaluate(self.mapping._starting, self.data, plot.environment)
    [261](https://file+.vscode-resource.vscode-cdn.net/Users/machow/repos/plotnine-guide/~/.virtualenvs/plotnine-guide/lib/python3.9/site-packages/plotnine/layer.py:261)     evaled_aes = aes(**{str(col): col for col in evaled})
    [262](https://file+.vscode-resource.vscode-cdn.net/Users/machow/repos/plotnine-guide/~/.virtualenvs/plotnine-guide/lib/python3.9/site-packages/plotnine/layer.py:262)     plot.scales.add_defaults(evaled, evaled_aes)

File [~/.virtualenvs/plotnine-guide/lib/python3.9/site-packages/plotnine/mapping/evaluation.py:251](https://file+.vscode-resource.vscode-cdn.net/Users/machow/repos/plotnine-guide/~/.virtualenvs/plotnine-guide/lib/python3.9/site-packages/plotnine/mapping/evaluation.py:251), in evaluate(aesthetics, data, env)
    [249](https://file+.vscode-resource.vscode-cdn.net/Users/machow/repos/plotnine-guide/~/.virtualenvs/plotnine-guide/lib/python3.9/site-packages/plotnine/mapping/evaluation.py:249)     else:
    [250](https://file+.vscode-resource.vscode-cdn.net/Users/machow/repos/plotnine-guide/~/.virtualenvs/plotnine-guide/lib/python3.9/site-packages/plotnine/mapping/evaluation.py:250)         msg = f"Do not know how to deal with aesthetic '{ae}'"
--> [251](https://file+.vscode-resource.vscode-cdn.net/Users/machow/repos/plotnine-guide/~/.virtualenvs/plotnine-guide/lib/python3.9/site-packages/plotnine/mapping/evaluation.py:251)         raise PlotnineError(msg)
    [253](https://file+.vscode-resource.vscode-cdn.net/Users/machow/repos/plotnine-guide/~/.virtualenvs/plotnine-guide/lib/python3.9/site-packages/plotnine/mapping/evaluation.py:253) # Using `type` preserves the subclass of pd.DataFrame
    [254](https://file+.vscode-resource.vscode-cdn.net/Users/machow/repos/plotnine-guide/~/.virtualenvs/plotnine-guide/lib/python3.9/site-packages/plotnine/mapping/evaluation.py:254) index = data.index if len(data.index) and evaled else None

PlotnineError: "Do not know how to deal with aesthetic 'color'"

Note on None in other aesthetics

It looks like passing a None directly to an aesthetic mapping doesn't work for other aesthetics (e.g. aes(shape=None)). But this seems like it would be highly unusual for people to do.