[tor-commits] [stem/master] Proper hash function for ExitPolicy

[atagar at torproject.org]

commit d76ced9fbc1408472de5a08b15789bbb1bccc6c0
Author: Damian Johnson <atagar at torproject.org>
Date:   Fri Sep 5 08:52:37 2014 -0700

    Proper hash function for ExitPolicy
    
    We skipped on implementing hash() out of concern of a circular dependency from
    @lru_cache on _get_rules(). But _get_rules() no longer uses @lru_cache there
    due to pickleability so we can now implement hash().
---
 stem/exit_policy.py |   15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/stem/exit_policy.py b/stem/exit_policy.py
index 86722af..1f72b60 100644
--- a/stem/exit_policy.py
+++ b/stem/exit_policy.py
@@ -235,6 +235,7 @@ class ExitPolicy(object):
       self._input_rules = rules
 
     self._rules = None
+    self._hash = None
 
     # Result when no rules apply. According to the spec policies default to 'is
     # allowed', but our microdescriptor policy subclass might want to change
@@ -435,12 +436,16 @@ class ExitPolicy(object):
     return ', '.join([str(rule) for rule in self._get_rules()])
 
   def __hash__(self):
-    # TODO: It would be nice to provide a real hash function, but doing so is
-    # tricky due to how we lazily load the rules. Like equality checks a proper
-    # hash function would need to call _get_rules(), but that's behind
-    # @lru_cache which calls hash() forming a circular dependency.
+    if self._hash is None:
+      my_hash = 0
+
+      for rule in self._get_rules():
+        my_hash *= 1024
+        my_hash += hash(rule)
+
+      self._hash = my_hash
 
-    return id(self)
+    return self._hash
 
   def __eq__(self, other):
     if isinstance(other, ExitPolicy):