Matplotlib
The most widely used Python plotting library - substrate for most other plot libs.
- Two APIs: pyplot (stateful) and OO (fig/ax).
- pandas and seaborn render through it.
- Production scripts prefer the OO API.
When to use: Training curves, ROC plots, EDA - anywhere a figure is needed.
Example: fig, ax = plt.subplots(); ax.plot(epochs, loss); ax.set_xlabel("epoch"); fig.savefig("loss.png").