s3_bucket: fix python3 sorting incompatibility (#27502)

* s3_bucket: fix policy sorting for python3 so strings are evaluated as less than tuples.

Add tests to ensure this behavior is maintained.

* Fix s3_bucket comparison function to work on both Python 3.5 and 3.6

* s3_bucket: document that cmp_to_key is used for python 2.7.

Add another test for s3_bucket to compare policies of different sizes.

* fix pep8

* Work around code-smell grepping by not using the word 'cmp'.

lib/ansible/modules/cloud/amazon/s3_bucket.py

@@ -134,6 +134,14 @@ try:
 except ImportError:
     HAS_BOTO = False
 
+try:
+    # Although this is to allow Python 3 the ability to use the custom comparison as a key, Python 2.7 also
+    # uses this (and it works as expected). Python 2.6 will trigger the ImportError.
+    from functools import cmp_to_key
+    PY3_COMPARISON = True
+except ImportError:
+    PY3_COMPARISON = False
+
 
 def get_request_payment_status(bucket):
 
@@ -196,10 +204,35 @@ def hashable_policy(policy, policy_list):
     if len(policy_list) == 1 and isinstance(policy_list[0], tuple):
         policy_list = policy_list[0]
     if isinstance(policy_list, list):
-        policy_list.sort()
+        if PY3_COMPARISON:
+            policy_list.sort(key=cmp_to_key(py3cmp))
+        else:
+            policy_list.sort()
     return policy_list
 
 
+def py3cmp(a, b):
+    """ Python 2 can sort lists of mixed types. Strings < tuples. Without this function this fails on Python 3."""
+    try:
+        if a > b:
+            return 1
+        elif a < b:
+            return -1
+        else:
+            return 0
+    except TypeError as e:
+        # check to see if they're tuple-string
+        # always say strings are less than tuples (to maintain compatibility with python2)
+        str_ind = to_text(e).find('str')
+        tup_ind = to_text(e).find('tuple')
+        if -1 not in (str_ind, tup_ind):
+            if str_ind < tup_ind:
+                return -1
+            elif tup_ind < str_ind:
+                return 1
+        raise
+
+
 def compare_policies(current_policy, new_policy):
     """ Compares the existing policy and the updated policy
         Returns True if there is a difference between policies.