Use shutil.which() in subprocess.check_call() when executing mamba/micromamba/conda (#103)

* Use shutil.which() in subprocess.check_call()

* simplify package manager detection

Author: vasiljevic

.gitignore

@@ -124,3 +124,6 @@ src/web_worker_kernel.ts
 
 # Labextension
 share
+
+# venv
+.venv

jupyterlite_xeus_python/env_build_addon.py

@@ -47,24 +47,11 @@
 except ImportError:
     MAMBA_PYTHON_AVAILABLE = False
 
-try:
-    check_call(["mamba", "--version"], **SILENT)
-    MAMBA_AVAILABLE = True
-except FileNotFoundError:
-    MAMBA_AVAILABLE = False
-
-try:
-    check_call(["micromamba", "--version"], **SILENT)
-    MICROMAMBA_AVAILABLE = True
-except FileNotFoundError:
-    MICROMAMBA_AVAILABLE = False
+MAMBA_COMMAND = shutil.which("mamba")
 
-try:
-    check_call(["conda", "--version"], **SILENT)
-    CONDA_AVAILABLE = True
-except FileNotFoundError:
-    CONDA_AVAILABLE = False
+MICROMAMBA_COMMAND = shutil.which("micromamba")
 
+CONDA_COMMAND = shutil.which("conda")
 
 class PackagesList(List):
     def from_string(self, s):
@@ -252,15 +239,15 @@ def create_env(self):
         for channel in self.channels:
             channels.extend(["-c", channel])
 
-        if MAMBA_AVAILABLE:
+        if MAMBA_COMMAND:
             # Mamba needs the directory to exist already
             self.prefix_path.mkdir(parents=True, exist_ok=True)
-            return self._create_env_with_config("mamba", channels)
+            return self._create_env_with_config(MAMBA_COMMAND, channels)
 
-        if MICROMAMBA_AVAILABLE:
+        if MICROMAMBA_COMMAND:
             run(
                 [
-                    "micromamba",
+                    MICROMAMBA_COMMAND,
                     "create",
                     "--yes",
                     "--root-prefix",
@@ -276,8 +263,8 @@ def create_env(self):
             )
             return
 
-        if CONDA_AVAILABLE:
-            return self._create_env_with_config("conda", channels)
+        if CONDA_COMMAND:
+            return self._create_env_with_config(CONDA_COMMAND, channels)
 
         raise RuntimeError(
             """Failed to create the virtual environment for xeus-python,