added basic run single hook implmentation

pre_commit/languages/python.py

@@ -15,6 +15,10 @@ def in_env():
 
 def install_environment():
     assert local.path('setup.py').exists()
+    # Return immediately if we already have a virtualenv
+    if local.path('py_env').exists():
+        return
+
     # Install a virtualenv
     local['virtualenv'][PY_ENV]()
 

pre_commit/run.py

@@ -1,20 +1,45 @@
 
 import argparse
+import os.path
 from pre_commit import git
+from pre_commit.clientlib.validate_config import validate_config
+from pre_commit.repository import Repository
 
 def install():
     """Install the pre-commit hook."""
     git.create_pre_commit()
 
+
 def uninstall():
     """Uninstall the pre-commit hook."""
-    raise NotImplementedError
+    git.remove_pre_commit()
 
 
 def run_hooks(arguments):
     """Actually run the hooks."""
     raise NotImplementedError
 
+def run_single_hook(hook_id):
+    configs = validate_config([])
+    for config in configs:
+        repo = Repository(config)
+        if hook_id in repo.hooks:
+            repo.install()
+
+            retcode, stdout, stderr = repo.run_hook(hook_id, map(os.path.abspath, ['pre_commit/constants.py']))
+
+            if retcode != repo.hooks[hook_id].get('expected_return_value', 0):
+                for out in (stdout, stderr):
+                    out = out.rstrip()
+                    if len(out) > 0:
+                        print out
+                return 1
+            else:
+                return 0
+    else:
+        print "No hook with id {0}".format(hook_id)
+        return 1
+
 
 def run(argv):
     parser = argparse.ArgumentParser()
@@ -30,6 +55,10 @@ def run(argv):
         action='store_true',
         help='Uninstall the pre-commit script.',
     )
+    group.add_argument(
+        '-r', '--run',
+        help='Run a hook'
+    )
 
     args = parser.parse_args(argv)
 
@@ -37,5 +66,7 @@ def run(argv):
         return install()
     elif args.uninstall:
         return uninstall()
+    elif args.run:
+        return run_single_hook(args.run)
     else:
         return run_hooks(args)