Custom yaml Loader

Instead of monkeypatching the yaml Loader in an attempt to avoid parsing numbers make a custom Loader where the float/int tags are entirely removed.

conda_build/metadata.py

@@ -1,7 +1,6 @@
 from __future__ import absolute_import, division, print_function
 
 from collections import OrderedDict
-import contextlib
 import copy
 import hashlib
 import json
@@ -35,9 +34,42 @@
              'files of conda recipes)')
 
 try:
-    loader = yaml.CLoader
-except:
-    loader = yaml.Loader
+    Loader = yaml.CLoader
+except AttributeError:
+    Loader = yaml.Loader
+
+
+class StringifyNumbersLoader(Loader):
+    @classmethod
+    def remove_implicit_resolver(cls, tag):
+        if 'yaml_implicit_resolvers' not in cls.__dict__:
+            cls.yaml_implicit_resolvers = {
+                k: v[:]
+                for k, v in cls.yaml_implicit_resolvers.items()
+            }
+        for ch in tuple(cls.yaml_implicit_resolvers):
+            resolvers = [
+                (t, r)
+                for t, r in cls.yaml_implicit_resolvers[ch]
+                if t != tag
+            ]
+            if resolvers:
+                cls.yaml_implicit_resolvers[ch] = resolvers
+            else:
+                del cls.yaml_implicit_resolvers[ch]
+
+    @classmethod
+    def remove_constructor(cls, tag):
+        if 'yaml_constructors' not in cls.__dict__:
+            cls.yaml_constructors = cls.yaml_constructors.copy()
+        if tag in cls.yaml_constructors:
+            del cls.yaml_constructors[tag]
+
+
+StringifyNumbersLoader.remove_implicit_resolver('tag:yaml.org,2002:float')
+StringifyNumbersLoader.remove_implicit_resolver('tag:yaml.org,2002:int')
+StringifyNumbersLoader.remove_constructor('tag:yaml.org,2002:float')
+StringifyNumbersLoader.remove_constructor('tag:yaml.org,2002:int')
 
 on_win = (sys.platform == 'win32')
 
@@ -222,9 +254,7 @@ def select_lines(data, namespace, variants_in_place):
 
 def yamlize(data):
     try:
-        with stringify_numbers():
-            loaded_data = yaml.load(data, Loader=loader)
-        return loaded_data
+        return yaml.load(data, Loader=StringifyNumbersLoader)
     except yaml.error.YAMLError as e:
         if '{{' in data:
             try:
@@ -884,20 +914,6 @@ def _hash_dependencies(hashing_dependencies, hash_length):
     return 'h{0}'.format(hash_.hexdigest())[:hash_length + 1]
 
 
-@contextlib.contextmanager
-def stringify_numbers():
-    # ensure that numbers are not interpreted as ints or floats.  That trips up versions
-    #     with trailing zeros.
-    implicit_resolver_backup = loader.yaml_implicit_resolvers.copy()
-    for ch in list(u'0123456789'):
-        if ch in loader.yaml_implicit_resolvers:
-            del loader.yaml_implicit_resolvers[ch]
-    yield
-    for ch in list(u'0123456789'):
-        if ch in implicit_resolver_backup:
-            loader.yaml_implicit_resolvers[ch] = implicit_resolver_backup[ch]
-
-
 class MetaData(object):
     def __init__(self, path, config=None, variant=None):