legend.py

# -*- coding: utf-8 -*-
# https://matplotlib.org/3.2.1/gallery/text_labels_and_annotations/legend.html

import sys

import numpy as np
from matplotlib.backends.backend_qt5agg import FigureCanvas
from matplotlib.figure import Figure
from PyQt5.QtWidgets import QApplication

app = QApplication(sys.argv)

fig = Figure(figsize=(8, 6))
canvas = FigureCanvas(fig)
canvas.resize(640, 480)
canvas.show()

# Make some fake data.
a = b = np.arange(0, 3, 0.02)
c = np.exp(a)
d = c[::-1]

# Create plots with pre-defined labels.
ax = fig.subplots()
ax.plot(a, c, "k--", label="Model length")
ax.plot(a, d, "k:", label="Data length")
ax.plot(a, c + d, "k", label="Total message length")

legend = ax.legend(loc="upper center", shadow=True, fontsize="x-large")

# Put a nicer background color on the legend.
legend.get_frame().set_facecolor("C0")

sys.exit(app.exec_())