Load only requested command module in shub.tool and shub.image

shub/image/__init__.py

@@ -1,5 +1,7 @@
-import click
 import importlib
+import sys
+
+import click
 
 
 @click.group(help="Manage project based on custom Docker image")
@@ -18,6 +20,9 @@ def cli():
     "check",
 ]
 
+if len(sys.argv) > 2 and sys.argv[2] in module_deps:
+    module_deps = [sys.argv[2]]
+
 for command in module_deps:
     module_path = "shub.image." + command
     command_module = importlib.import_module(module_path)

shub/tool.py

@@ -1,5 +1,6 @@
 from __future__ import absolute_import
 import importlib
+import sys
 
 import click
 
@@ -51,6 +52,12 @@ def cli():
     "image",
 ]
 
+# Some imports, particularly requests and pip, are very slow. To avoid
+# importing these modules when running a command that doesn't need them, we
+# import that command module only.
+if len(sys.argv) > 1 and sys.argv[1] in commands:
+    commands = [sys.argv[1]]
+
 for command in commands:
     module_path = "shub." + command
     command_module = importlib.import_module(module_path)