Number of subplots in mpl.axes.Subplot object

From an `mpl.axes.Subplot` `obj`, I can find out information about the grid pattern via
```python
geom = obj \
    .get_subplotspec() \
    .get_topmost_subplotspec()\
    .get_geometry()
```
For example, the product `geom[0] * geom[1]` gives the maximum number of subplots in the grid.

_Q:_ Is there a way for finding out how many subplots there _actually_ are?