diff mercurial/thirdparty/attr/converters.py @ 34397:765eb17a7eb8

thirdparty: vendor attrs

The attrs package allows defining namedtuple-like classes with no weird
behavior and no runtime performance cost.

This patch vendors in attrs 17.2.0.

# no-check-commit

Differential Revision: https://phab.mercurial-scm.org/D867

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/mercurial/thirdparty/attr/converters.py	Sun Oct 01 04:14:16 2017 -0700
@@ -0,0 +1,24 @@
+"""
+Commonly useful converters.
+"""
+
+from __future__ import absolute_import, division, print_function
+
+
+def optional(converter):
+    """
+    A converter that allows an attribute to be optional. An optional attribute
+    is one which can be set to ``None``.
+
+    :param callable converter: the converter that is used for non-``None``
+        values.
+
+    ..  versionadded:: 17.1.0
+    """
+
+    def optional_converter(val):
+        if val is None:
+            return None
+        return converter(val)
+
+    return optional_converter