merge PR27 improving startup time0.15.39

1 files changed, 33 insertions, 0 deletions

diff --git a/util.py b/util.py
index 9f939cf..e5e816f 100644
--- a/util.py
+++ b/util.py
@@ -6,6 +6,9 @@ some helper functions that might be generally useful
 
 from __future__ import absolute_import, print_function
 
+from functools import partial
+import re
+
 from .compat import text_type, binary_type
 
 if False:  # MYPY
@@ -13,6 +16,36 @@ if False:  # MYPY
     from .compat import StreamTextType  # NOQA
 
 
+class LazyEval(object):
+    """
+    Lightweight wrapper around lazily evaluated func(*args, **kwargs).
+
+    func is only evaluated when any attribute of its return value is accessed.
+    Every attribute access is passed through to the wrapped value.
+    (This only excludes special cases like method-wrappers, e.g., __hash__.)
+    The sole additional attribute is the lazy_self function which holds the
+    return value (or, prior to evaluation, func and arguments), in its closure.
+    """
+    def __init__(self, func, *args, **kwargs):
+        def lazy_self():
+            return_value = func(*args, **kwargs)
+            object.__setattr__(self, "lazy_self", lambda: return_value)
+            return return_value
+        object.__setattr__(self, "lazy_self", lazy_self)
+
+    def __getattribute__(self, name):
+        lazy_self = object.__getattribute__(self, "lazy_self")
+        if name == "lazy_self":
+            return lazy_self
+        return getattr(lazy_self(), name)
+
+    def __setattr__(self, name, value):
+        setattr(self.lazy_self(), name, value)
+
+
+RegExp = partial(LazyEval, re.compile)
+
+
 # originally as comment
 # https://github.com/pre-commit/pre-commit/pull/211#issuecomment-186466605
 # if you use this in your code, I suggest adding a test in your test suite