Add experimental support for python in 'git cl format'

git_cl.py

Index: git_cl.py
diff --git a/git_cl.py b/git_cl.py
index ce365419b279a84dd43970244e43942b09515262..26f04fd8c8289ba838902f272f11346a7ef626c3 100755
--- a/git_cl.py
+++ b/git_cl.py
@@ -3183,12 +3183,14 @@ def BuildGitDiffCmd(diff_type, upstream_commit, args, extensions):
 
 @subcommand.usage('[files or directories to diff]')
 def CMDformat(parser, args):
-  """Runs clang-format on the diff."""
+  """Runs auto-formatting tools (clang-format etc.) on the diff."""
   CLANG_EXTS = ['.cc', '.cpp', '.h', '.mm', '.proto', '.java']
   parser.add_option('--full', action='store_true',
                     help='Reformat the full content of all touched files')
   parser.add_option('--dry-run', action='store_true',
                     help='Don\'t modify any file on disk.')
+  parser.add_option('--python', action='store_true',
+                    help='Format python code with yapf (experimental).')
   parser.add_option('--diff', action='store_true',
                     help='Print diff to stdout rather than modifying files.')
   opts, args = parser.parse_args(args)
@@ -3216,12 +3218,12 @@ def CMDformat(parser, args):
 
   if opts.full:
     # Only list the names of modified files.
-    clang_diff_type = '--name-only'
+    diff_type = '--name-only'
   else:
     # Only generate context-less patches.
-    clang_diff_type = '-U0'
+    diff_type = '-U0'
 
-  diff_cmd = BuildGitDiffCmd(clang_diff_type, upstream_commit, args, CLANG_EXTS)
+  diff_cmd = BuildGitDiffCmd(diff_type, upstream_commit, args, CLANG_EXTS)
   diff_output = RunGit(diff_cmd)
 
   top_dir = os.path.normpath(
@@ -3267,6 +3269,29 @@ def CMDformat(parser, args):
     if opts.dry_run and len(stdout) > 0:
       return_value = 2
 
+  # Similar code to above, but using yapf on .py files rather than clang-format
+  # on C/C++ files
+  if opts.python:
+    diff_cmd = BuildGitDiffCmd(diff_type, upstream_commit, args, ['.py'])
+    diff_output = RunGit(diff_cmd)
+    yapf_tool = gclient_utils.FindExecutable('yapf')
+    if yapf_tool is None:
+      DieWithError('yapf not found in PATH')
+
+    if opts.full:
+      files = diff_output.splitlines()
+      if files:
+        cmd = [yapf_tool]
+        if not opts.dry_run and not opts.diff:
+          cmd.append('-i')
+        stdout = RunCommand(cmd + files, cwd=top_dir)
+        if opts.diff:
+          sys.stdout.write(stdout)
+    else:
+      # TODO(sbc): yapf --lines mode still has some issues.
+      # https://github.com/google/yapf/issues/154
+      DieWithError('--python currently only works with --full')
+
   # Build a diff command that only operates on dart files. dart's formatter
   # does not have the nice property of only operating on modified chunks, so
   # hard code full.