Fix python version enforcement when no environment file

Author: jder

asv/plugins/conda.py

@@ -136,7 +136,9 @@ def _setup(self):
         conda_args = [util.replace_python_version(arg, self._python) for arg in conda_args]
 
         if not self._conda_environment_file:
-            conda_args = ['wheel', 'pip'] + conda_args
+            # With a user-provided envronment, we assume it specifies a python version;
+            # without an environment.yml file, we need to add the python version ourselves
+            conda_args = [f'python={self._python}', 'wheel', 'pip'] + conda_args
 
         # Create a temporary environment.yml file
         # and use that to generate the env for benchmarking.

asv/plugins/mamba.py

@@ -138,8 +138,8 @@ def _setup(self):
         env.update(self.build_env_vars)
         Path(f"{self._path}/conda-meta").mkdir(parents=True, exist_ok=True)
         if not self._mamba_environment_file:
-            # Construct payload
-            mamba_pkgs = ["wheel", "pip"]
+            # Construct payload; since there is no environment.yml file, we need to add the python version ourselves
+            mamba_pkgs = [f"python={self._python}", "wheel", "pip"]
         else:
             # For named environments
             env_file_name = self._mamba_environment_file