Move conda wrappers to their own module

tljh/conda.py

@@ -0,0 +1,48 @@
+"""
+Wrap conda commandline program
+"""
+import os
+import subprocess
+import json
+
+
+def ensure_conda_env(prefix):
+    """
+    Ensure a conda environment in the prefix
+    """
+    abspath = os.path.abspath(prefix)
+    try:
+        output = json.loads(
+            subprocess.check_output(['conda', 'create', '--json', '--prefix', abspath]).decode()
+        )
+    except subprocess.CalledProcessError as e:
+        output = json.loads(e.output.decode())
+        if 'error' in output and output['error'] == f'CondaValueError: prefix already exists: {abspath}':
+            return
+        raise
+    if 'success' in output and output['success'] == True:
+        return
+
+
+def ensure_conda_packages(prefix, packages):
+    """
+    Ensure packages are installed in the conda prefix
+    """
+    abspath = os.path.abspath(prefix)
+    # Let subprocess errors propagate
+    # FIXME: raise different exception when using
+    raw_output = subprocess.check_output([
+        'conda', 'install',
+        '--json',
+        '--prefix', abspath
+    ] + packages).decode()
+    # `conda install` outputs JSON lines for fetch updates,
+    # and a undelimited output at the end. There is no reasonable way to
+    # parse this outside of this kludge.
+    filtered_output = '\n'.join([
+        l for l in raw_output.split('\n')
+        if not l.startswith('{"fetch"')
+    ])
+    output = json.loads(filtered_output)
+    if 'success' in output and output['success'] == True:
+        return