Import error from `tlz` when `cytoolz` not installed

[jrbourbeau]

Today I created a minimal environment like this

mamba create -n test python=3.12 ipython
mamba activate test
pip install toolz

and then attempt to make this import from tlz: from tlz import groupby, merge and got this error

In [1]: from tlz import groupby, merge
---------------------------------------------------------------------------
ImportError                               Traceback (most recent call last)
Cell In[1], line 1
----> 1 from tlz import groupby, merge

File ~/mambaforge/envs/test6/lib/python3.12/site-packages/tlz/_build_tlz.py:55, in TlzLoader.exec_module(self, module)
     54 def exec_module(self, module):
---> 55     toolz_mods = self._load_toolz(module.__name__)
     56     fast_mod = toolz_mods.get('cytoolz') or toolz_mods['toolz']
     57     slow_mod = toolz_mods.get('toolz') or toolz_mods['cytoolz']

File ~/mambaforge/envs/test6/lib/python3.12/site-packages/tlz/_build_tlz.py:29, in TlzLoader._load_toolz(self, fullname)
     27     pass
     28 if not rv:
---> 29     raise ImportError(fullname)
     30 return rv

ImportError: tlz.groupby

If I then install cytoolz, the error goes away. I came across this because from tlz import groupby, merge gets run as part of import dask

cc @eriknw in case you have any idea what's going on here

[eriknw]

Oh my! I'll take a look. I thought tests would catch this? This code hasn't been updated in a while. I think there's still 2.7-specific code that can be removed.

[jrbourbeau]

I'm actually now unsure if this is just me or not. I asked some coworkers to try and reproduce, but they're not able to. Also, nobody has opened an issue in dask for this, which surprised me. I tried again after clearing my local conda cache, but am still seeing the same error... 🤷