benchmark.Compare raises: TypeError: object of type 'NoneType' has no len()

[ezyang]

Traceback (most recent call last):
  File "test.py", line 12, in <module>
    compare.print()
  File "/Users/ezyang/miniconda3/lib/python3.7/site-packages/torch/utils/benchmark/utils/compare.py", line 298, in print
    print(str(self))
  File "/Users/ezyang/miniconda3/lib/python3.7/site-packages/torch/utils/benchmark/utils/compare.py", line 278, in __str__
    return "\n".join(self._render())
  File "/Users/ezyang/miniconda3/lib/python3.7/site-packages/torch/utils/benchmark/utils/compare.py", line 305, in _render
    output.append(self._layout(group))
  File "/Users/ezyang/miniconda3/lib/python3.7/site-packages/torch/utils/benchmark/utils/compare.py", line 321, in _layout
    return table.render()
  File "/Users/ezyang/miniconda3/lib/python3.7/site-packages/torch/utils/benchmark/utils/compare.py", line 252, in render
    col_widths = [max(len(j) for j in i) for i in zip(*string_rows)]
  File "/Users/ezyang/miniconda3/lib/python3.7/site-packages/torch/utils/benchmark/utils/compare.py", line 252, in <listcomp>
    col_widths = [max(len(j) for j in i) for i in zip(*string_rows)]
  File "/Users/ezyang/miniconda3/lib/python3.7/site-packages/torch/utils/benchmark/utils/compare.py", line 252, in <genexpr>
    col_widths = [max(len(j) for j in i) for i in zip(*string_rows)]
TypeError: object of type 'NoneType' has no len()
(base) ezyang-mbp:~ ezyang$ cat test.py
import torch
import torch.utils.benchmark as benchmark

results = []
results.append(benchmark.Timer(
    stmt='2',
    label='foo',
    sub_label='bar',
).blocked_autorange(min_run_time=1))

compare = benchmark.Compare(results)
compare.print()

I know how to fix it (add description) but it shouldn't raise an uninterpretable error like this.

[ezyang]

cc @robieta

[robieta]

Yeah, the internals of Compare are kind of horrible. I should dust off #54010.

[matham]

Did you figure out what the actual problem is/workaround?

[akihironitta]

I remember I needed to provide a string to description as stated in the issue description.