ValueError: cannot have more than one handle with the same label

ValueError: cannot have more than one handle with the same label

$ python -c "import matplotlib.pyplot as plt; plt.plot([1,2], label='A'); plt.plot([2,3], label='A'); plt.legend()"
Traceback (most recent call last):
  File "<string>", line 1, in <module>
ValueError: cannot have more than one handle with the same label

Why this happens

Legend tries to resolve duplicate labels when you manually provide handles/labels or certain settings.

Fix

Use unique labels or filter duplicates before passing to legend.

Wrong code

import matplotlib.pyplot as plt
plt.plot([1,2], label='A')
plt.plot([2,3], label='A')
plt.legend()

Fixed code

import matplotlib.pyplot as plt
line1, = plt.plot([1,2], label='A')
line2, = plt.plot([2,3], label='B')
handles = {l.get_label(): l for l in [line1, line2]}
plt.legend(handles.values())
plt.show()