conda returns 'Solving environment: failed'

DELETE to C:\Users\<YOUR_USERNAME>\.condarc and then update Conda. This will solve it in Windows.

conda update conda

thank you, that works ! in case the link grows old, here is the simplified copy:

1. Navigate to your conda base environment, as given by conda info.
2. Open the file lib/pythonX.Y/site-packages/conda/gateways/connection/init.py. Where X.Y is the python major-minor version.

3. Replace the function 'should_bypass_proxies_patched' with :

   def should_bypass_proxies_patched(should_bypass_proxies_func, url, no_proxy=None):
       if url.startswith("file://"):
           return True
       try:
           return should_bypass_proxies_func(url, no_proxy)
       except TypeError:
           return should_bypass_proxies_func(url)
   

Downgrading to conda 4.5.5 fixed this for me.

And with a ranting hat on: This is the third time in the space of about 18 months that a conda update has resulted in an error that causes builds to fail, and there's been plenty of other issues too. I presume it will be fixed by the core conda people at some point, and maybe it is caused by a particular combination of third party dependencies, but one way or another conda always seems extremely buggy. There was once an update that caused conda install conda to delete itself!