A really basic git module. Improvements welcome.

library/git

+#!/usr/bin/python
+
+# I wanted to keep this simple at first, so for now this checks out
+# from the MASTER branch of a repo at a particular SHA or
+# tag.  Latest is not supported, you should not be doing
+# that.  Branch checkouts are not supported.  Contribs
+# welcome! -- MPD
+
+try:
+    import json
+except ImportError:
+    import simplejson as json
+import os
+import sys
+import shlex
+import subprocess
+
+# ===========================================
+# convert arguments of form ensure=running name=foo
+# to a dictionary
+# FIXME: make more idiomatic
+
+args = " ".join(sys.argv[1:])
+items = shlex.split(args)
+params = {}
+for x in items:
+    (k, v) = x.split("=")
+    params[k] = v
+
+dest = params['dest']
+repo = params['repo']
+version = params['version']
+
+# ===========================================
+
+def get_version(dest):
+   ''' samples the version of the git repo '''
+   os.chdir(dest)
+   cmd = "git show --abbrev-commit"
+   sha = os.popen(cmd).read().split("\n")
+   sha = sha[0].split()[1]
+   return sha
+
+def clone(repo, dest):
+   ''' makes a new git repo if it does not already exist '''
+   try:
+       os.makedirs(dest)
+   except:
+       pass
+   cmd = "git clone %s %s" % (repo, dest)
+   cmd = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+   return cmd.communicate()
+
+def pull(repo, dest):
+   ''' updates repo from remote sources '''
+   os.chdir(dest)
+   cmd = "git pull -u origin"
+   cmd = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+   return cmd.communicate()
+
+def switchver(version, dest):
+   ''' once pulled, switch to a particular SHA or tag '''
+   os.chdir(dest)
+   if version != 'HEAD':
+      cmd = "git checkout %s --force" % version
+   else:
+      # is there a better way to do this?
+      cmd = "git rebase origin"
+   cmd = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+   (out, err) = cmd.communicate()
+   return (out, err)
+ 
+
+gitconfig = os.path.join(dest, '.git', 'config')
+
+out, err, status = (None, None, None)
+
+# if there is no git configuration, do a clone operation
+# else pull and switch the version
+
+before = None
+if not os.path.exists(gitconfig):
+   (out, err) = clone(repo, dest)
+else:
+   # else do a pull   
+   before = get_version(dest)
+   (out, err) = pull(repo, dest)
+
+# handle errors from clone or pull
+
+if out.find('error') != -1:
+   print json.dumps({
+       "failed" : True,
+       "out"    : out,
+       "err"    : err
+   })
+   sys.exit(1)
+
+# switch to version specified regardless of whether
+# we cloned or pulled
+
+(out, err) = switchver(version, dest)
+if err.find('error') != -1:
+   print json.dumps({
+       "failed" : True,
+       "out"    : out,
+       "err"    : err
+   })
+   sys.exit(1)
+
+# determine if we changed anything
+
+after = get_version(dest)
+changed = False
+
+if before != after:
+   changed = True
+
+print json.dumps({
+   "changed" : changed,
+   "before"  : before,
+   "after"   : after
+})
+