On PyPy builtins[key] should be builtins.key, which is also CPython compatible. This is a continuation of the fix(es) in issues #7186, #7272
lib/matplotlib/axes/axes.py line 6105
lib/matplotlib/axes/_axes.py line 6477
range = __builtins__['range'] -> range = __builtins__.range

For reference, this turned up in testing pandas/tests/plotting