Only show a legend when the matplotlib figure has one

[robertoffmoura]

Converted matplotlib figures without legends unexpectedly show legends in plotly. mpl_to_plotly left layout.showlegend unset, and plotly.js defaults it to True, auto-naming unnamed traces, so every conversion without an explicit mpl legend (e.g. plt.plot(x, y) with no labels, boxplots) rendered with a legend of junk entries.

Fix:

• open_figure now sets showlegend=False by default; the legend is only enabled by open_legend when the matplotlib figure actually has one (existing behavior, unchanged)

Snippet to reproduce:

import matplotlib
matplotlib.use("Agg")
import matplotlib.pyplot as plt
import plotly.tools as tls

fig, ax = plt.subplots()
ax.plot([0, 1, 2, 3], [0, 1, 0, 1], "b", [0, 1, 2, 3], [1, 0, 1, 0], "r--")
fig.savefig("legend_mpl.png")

p = tls.mpl_to_plotly(fig)
p.write_image("legend_plotly.png")

matplotlib	plotly before	plotly after

[camdecoster]

This looks good, but does it handle the case when a plot has a legend enabled?

Could you please add a changelog entry?

[robertoffmoura]

Thank you. I've added a changelog entry.

Yes, it handles the case when a plot has a legend enabled. This behaviour is covered by tests in plotly/matplotlylib/tests/test_renderer.py:

• test_native_legend_enabled_when_matplotlib_legend_present
• test_multiple_traces_native_legend

[camdecoster]

What about the case of a figure with a legend, but where a line doesn't have a label?

[robertoffmoura]

Sorry, I misunderstood the previous comment. I just pushed a change to hide legend entries of unlabelled lines but keep those of labelled ones.

snippet to verify:

import matplotlib.pyplot as plt
import plotly.tools as tls

fig, ax = plt.subplots()
ax.plot([0, 1, 2], [0, 1, 2], label="Labeled line", color="blue")
ax.plot([0, 1, 2], [2, 1, 0], color="red")  # Unlabeled line
ax.legend()

# Save matplotlib reference
fig.savefig("legend_unlabeled_line_mpl.png", bbox_inches="tight")

# Convert and save plotly version
plotly_fig = tls.mpl_to_plotly(fig)
plotly_fig.write_image("legend_unlabeled_line_plotly.png")