Description: Make ordering and date in documentation reproducible

Author: Rebecca N. Palmer <rebecca_palmer@zoho.com>, Chris Lamb
Forwarded: no

--- a/openpyxl/descriptors/base.py
+++ b/openpyxl/descriptors/base.py
@@ -118,20 +118,23 @@ class MinMax(Min, Max):
 
 
 class Set(Descriptor):
-    """Value can only be from a set of know values"""
+    """Value can only be from a set of known values"""
 
     def __init__(self, name=None, **kw):
         if not 'values' in kw:
             raise TypeError("missing set of values")
         kw['values'] = set(kw['values'])
         super().__init__(name, **kw)
-        self.__doc__ = "Value must be one of {0}".format(self.values)
+        self.__doc__ = "Value must be one of {0}".format(sorted(self.values, key=str))
 
     def __set__(self, instance, value):
         if value not in self.values:
             raise ValueError(self.__doc__)
         super().__set__(instance, value)
 
+    def __repr__(self): # has <> because it may not reproduce the object, as name or subclass kwargs may be in use
+        return "<{0}(values={1})>".format(type(self), sorted(self.values, key=str))
+
 
 class NoneSet(Set):
 
--- a/doc/conf.py
+++ b/doc/conf.py
@@ -68,9 +68,13 @@ master_doc = 'index'
 
 # General information about the project.
 project = u'openpyxl'
-from datetime import date
+import datetime
+import time
+import os
+source_date = datetime.datetime.utcfromtimestamp(int(os.environ.get('SOURCE_DATE_EPOCH',time.time())))
 
-copyright = u'2010 - {0}, {1}'.format(date.today().year, openpyxl.__author__)
+
+copyright = u'2010 - {0}, {1}'.format(source_date.year, openpyxl.__author__)
 
 # The version info for the project you're documenting, acts as replacement for
 # |version| and |release|, also used in various other places throughout the