TypeError with scatterplot and label

Question

This seems pretty simple, but for some reason, I can't get it to work. This is in pandas 1.2.3 and matplotlib 3.4.0 running on an anaconda's python 3.8.8 on Windows 10 64-bit, inside a Jupyter notebook locally.

I've created a replication below. First, a working version; note the commented out label line:

import numpy as np
import pandas as pd
import matplotlib.pyplot as plt

df_test = pd.DataFrame(np.random.randn(1000, 4), columns=list("ABCD"))

df_test.plot(kind="scatter", x="A", y="B", 
             alpha=0.4,
             figsize=(10,7),
             #label="la la",
             s=df_test["C"]*100, 
             c="D", 
             cmap=plt.get_cmap("jet"), 
             colorbar=True,
)
plt.legend()

Running the above gives a complaint No handles with labels found to put in legend (as expected) and some deprecation warnings, but shows a chart. The dots are nicely colored, and you might even see the empty legend box.

Now, uncomment the label line:

df_test.plot(kind="scatter", x="A", y="B", 
             alpha=0.4,
             figsize=(10,7),
             label="la la",
             s=df_test["C"]*100, 
             c="D", 
             cmap=plt.get_cmap("jet"), 
             colorbar=True,
)
plt.legend()

and when I run this, I get a TypeError: object of type 'NoneType' has no len() error like the below:

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
D:\anaconda\envs\tf-gpu\lib\site-packages\IPython\core\formatters.py in __call__(self, obj)
    339                 pass
    340             else:
--> 341                 return printer(obj)
    342             # Finally look for special method names
    343             method = get_real_method(obj, self.print_method)

D:\anaconda\envs\tf-gpu\lib\site-packages\IPython\core\pylabtools.py in <lambda>(fig)
    246 
    247     if 'png' in formats:
--> 248         png_formatter.for_type(Figure, lambda fig: print_figure(fig, 'png', **kwargs))
    249     if 'retina' in formats or 'png2x' in formats:
    250         png_formatter.for_type(Figure, lambda fig: retina_figure(fig, **kwargs))

D:\anaconda\envs\tf-gpu\lib\site-packages\IPython\core\pylabtools.py in print_figure(fig, fmt, bbox_inches, **kwargs)
    130         FigureCanvasBase(fig)
    131 
--> 132     fig.canvas.print_figure(bytes_io, **kw)
    133     data = bytes_io.getvalue()
    134     if fmt == 'svg':

D:\anaconda\envs\tf-gpu\lib\site-packages\matplotlib\backend_bases.py in print_figure(self, filename, dpi, facecolor, edgecolor, orientation, format, bbox_inches, pad_inches, bbox_extra_artists, backend, **kwargs)
   2228                        else suppress())
   2229                 with ctx:
-> 2230                     self.figure.draw(renderer)
   2231 
   2232             if bbox_inches:

D:\anaconda\envs\tf-gpu\lib\site-packages\matplotlib\artist.py in draw_wrapper(artist, renderer, *args, **kwargs)
     72     @wraps(draw)
     73     def draw_wrapper(artist, renderer, *args, **kwargs):
---> 74         result = draw(artist, renderer, *args, **kwargs)
     75         if renderer._rasterizing:
     76             renderer.stop_rasterizing()

D:\anaconda\envs\tf-gpu\lib\site-packages\matplotlib\artist.py in draw_wrapper(artist, renderer, *args, **kwargs)
     49                 renderer.start_filter()
     50 
---> 51             return draw(artist, renderer, *args, **kwargs)
     52         finally:
     53             if artist.get_agg_filter() is not None:

D:\anaconda\envs\tf-gpu\lib\site-packages\matplotlib\figure.py in draw(self, renderer)
   2732 
   2733             self.patch.draw(renderer)
-> 2734             mimage._draw_list_compositing_images(
   2735                 renderer, self, artists, self.suppressComposite)
   2736 

D:\anaconda\envs\tf-gpu\lib\site-packages\matplotlib\image.py in _draw_list_compositing_images(renderer, parent, artists, suppress_composite)
    130     if not_composite or not has_images:
    131         for a in artists:
--> 132             a.draw(renderer)
    133     else:
    134         # Composite any adjacent images together

D:\anaconda\envs\tf-gpu\lib\site-packages\matplotlib\artist.py in draw_wrapper(artist, renderer, *args, **kwargs)
     49                 renderer.start_filter()
     50 
---> 51             return draw(artist, renderer, *args, **kwargs)
     52         finally:
     53             if artist.get_agg_filter() is not None:

D:\anaconda\envs\tf-gpu\lib\site-packages\matplotlib\_api\deprecation.py in wrapper(*inner_args, **inner_kwargs)
    429                          else deprecation_addendum,
    430                 **kwargs)
--> 431         return func(*inner_args, **inner_kwargs)
    432 
    433     return wrapper

D:\anaconda\envs\tf-gpu\lib\site-packages\matplotlib\axes\_base.py in draw(self, renderer, inframe)
   2923             renderer.stop_rasterizing()
   2924 
-> 2925         mimage._draw_list_compositing_images(renderer, self, artists)
   2926 
   2927         renderer.close_group('axes')

D:\anaconda\envs\tf-gpu\lib\site-packages\matplotlib\image.py in _draw_list_compositing_images(renderer, parent, artists, suppress_composite)
    130     if not_composite or not has_images:
    131         for a in artists:
--> 132             a.draw(renderer)
    133     else:
    134         # Composite any adjacent images together

D:\anaconda\envs\tf-gpu\lib\site-packages\matplotlib\artist.py in draw_wrapper(artist, renderer, *args, **kwargs)
     49                 renderer.start_filter()
     50 
---> 51             return draw(artist, renderer, *args, **kwargs)
     52         finally:
     53             if artist.get_agg_filter() is not None:

D:\anaconda\envs\tf-gpu\lib\site-packages\matplotlib\legend.py in draw(self, renderer)
    612 
    613         self.legendPatch.draw(renderer)
--> 614         self._legend_box.draw(renderer)
    615 
    616         renderer.close_group('legend')

D:\anaconda\envs\tf-gpu\lib\site-packages\matplotlib\offsetbox.py in draw(self, renderer)
    366         for c, (ox, oy) in zip(self.get_visible_children(), offsets):
    367             c.set_offset((px + ox, py + oy))
--> 368             c.draw(renderer)
    369 
    370         bbox_artist(self, renderer, fill=False, props=dict(pad=0.))

D:\anaconda\envs\tf-gpu\lib\site-packages\matplotlib\offsetbox.py in draw(self, renderer)
    366         for c, (ox, oy) in zip(self.get_visible_children(), offsets):
    367             c.set_offset((px + ox, py + oy))
--> 368             c.draw(renderer)
    369 
    370         bbox_artist(self, renderer, fill=False, props=dict(pad=0.))

D:\anaconda\envs\tf-gpu\lib\site-packages\matplotlib\offsetbox.py in draw(self, renderer)
    366         for c, (ox, oy) in zip(self.get_visible_children(), offsets):
    367             c.set_offset((px + ox, py + oy))
--> 368             c.draw(renderer)
    369 
    370         bbox_artist(self, renderer, fill=False, props=dict(pad=0.))

D:\anaconda\envs\tf-gpu\lib\site-packages\matplotlib\offsetbox.py in draw(self, renderer)
    366         for c, (ox, oy) in zip(self.get_visible_children(), offsets):
    367             c.set_offset((px + ox, py + oy))
--> 368             c.draw(renderer)
    369 
    370         bbox_artist(self, renderer, fill=False, props=dict(pad=0.))

D:\anaconda\envs\tf-gpu\lib\site-packages\matplotlib\offsetbox.py in draw(self, renderer)
    692             if self._clip_children and not (c.clipbox or c._clippath):
    693                 c.set_clip_path(tpath)
--> 694             c.draw(renderer)
    695 
    696         bbox_artist(self, renderer, fill=False, props=dict(pad=0.))

D:\anaconda\envs\tf-gpu\lib\site-packages\matplotlib\artist.py in draw_wrapper(artist, renderer, *args, **kwargs)
     49                 renderer.start_filter()
     50 
---> 51             return draw(artist, renderer, *args, **kwargs)
     52         finally:
     53             if artist.get_agg_filter() is not None:

D:\anaconda\envs\tf-gpu\lib\site-packages\matplotlib\collections.py in draw(self, renderer)
   1007     def draw(self, renderer):
   1008         self.set_sizes(self._sizes, self.figure.dpi)
-> 1009         super().draw(renderer)
   1010 
   1011 

D:\anaconda\envs\tf-gpu\lib\site-packages\matplotlib\artist.py in draw_wrapper(artist, renderer, *args, **kwargs)
     49                 renderer.start_filter()
     50 
---> 51             return draw(artist, renderer, *args, **kwargs)
     52         finally:
     53             if artist.get_agg_filter() is not None:

D:\anaconda\envs\tf-gpu\lib\site-packages\matplotlib\collections.py in draw(self, renderer)
    378         do_single_path_optimization = False
    379         if (len(paths) == 1 and len(trans) <= 1 and
--> 380                 len(facecolors) == 1 and len(edgecolors) == 1 and
    381                 len(self._linewidths) == 1 and
    382                 all(ls[1] is None for ls in self._linestyles) and

TypeError: object of type 'NoneType' has no len()

It seems to be an interaction with the c= for the coloring and the label= . If I comment out the color stuff (c=, cmap, colorbar), the plot renders with a legend box, and we saw that it also works with colors included and label commented out. I also tried restarting the kernel, and had same results. I have not tried making new environments with other versions yet, as I wanted to see if this was just me, or something others could replicate.

(BTW, On Colab, python 3.7.10, pandas 1.1.5, matplotlib 3.2.2, the code does appear to work (with a minor figsize complaint), so could be something about the more recent versions of these packages, or my setup...)

So, please be kind, but could anyone point out what silly thing I'm missing here? Any suggestions? Anyone able to replicate?

Answer 1

Possibly a bug in the older version, as it runs fine on recent versions of matplotlib. Recommend to just updating the matplotlib and pandas. Don't linger over it too much.