Improve performance on pre-commit -r pyflakes by 40%

pre_commit/git.py

@@ -1,14 +1,16 @@
 import os
 import pkg_resources
-
 from plumbum import local
 
+from pre_commit.util import memoize_by_cwd
 
-# TODO: optimization: memoize based on local.cwd.getpath()
+
+@memoize_by_cwd
 def get_root():
     return local['git']['rev-parse', '--show-toplevel']().strip()
 
 
+@memoize_by_cwd
 def get_pre_commit_path():
     return os.path.join(get_root(), '.git/hooks/pre-commit')
 
@@ -25,4 +27,4 @@ def remove_pre_commit():
 
 def get_head_sha(git_repo_path):
     with local.cwd(git_repo_path):
-        return (local['git']['rev-parse', 'HEAD'])().strip()
+        return (local['git']['rev-parse', 'HEAD'])().strip()

pre_commit/util.py

@@ -1,4 +1,8 @@
 
+import functools
+import os
+
+
 class cached_property(object):
     """Like @property, but caches the value."""
 
@@ -14,3 +18,19 @@ class cached_property(object):
         value = self._func(obj)
         obj.__dict__[self.__name__] = value
         return value
+
+
+def memoize_by_cwd(func):
+    """Memoize a function call based on os.getcwd()."""
+    cache = {}
+    @functools.wraps(func)
+    def wrapper(*args):
+        cwd = os.getcwd()
+        key = (cwd,) + args
+        try:
+            return cache[key]
+        except KeyError:
+            ret = cache[key] = func(*args)
+            return ret
+
+    return wrapper