Use dict comprehensions instead of dict constructor

PEP-0274 introduced dict comprehensions to replace dict constructor
with a sequence of key-value pair, these are benefits copied
from [1]:
  The dictionary constructor approach has two distinct disadvantages
  from the proposed syntax though.  First, it isn't as legible as a
  dict comprehension.  Second, it forces the programmer to create an
  in-core list object first, which could be expensive.
There is deep dive about PEP-0274[2] and basic tests about
performance[3].
Note: This commit doesn't handle dict constructor with kwagrs.

[1]http://legacy.python.org/dev/peps/pep-0274/
[2]http://doughellmann.com/2012/11/12/the-performance-impact-of-using-dict-instead-of-in-cpython-2-7-2.html
[3]http://paste.openstack.org/show/154798/

Change-Id: I45d0c289ecaf63a343fc9ad935cf2893d67d938a

rsdns/client/exceptions.py

@@ -23,7 +23,7 @@ class UnprocessableEntity(exceptions.ClientException):
     message = "Unprocessable Entity"
 
 
-_code_map = dict((c.http_status, c) for c in [UnprocessableEntity])
+_code_map = {c.http_status: c for c in [UnprocessableEntity]}
 
 
 def from_response(response, body):

trove/common/limits.py

@@ -56,7 +56,7 @@ class Limit(object):
         60 * 60 * 24: "DAY",
     }
 
-    UNIT_MAP = dict([(v, k) for k, v in UNITS.items()])
+    UNIT_MAP = {v: k for k, v in UNITS.items()}
 
     def __init__(self, verb, uri, regex, value, unit):
         """

trove/common/models.py

@@ -42,7 +42,7 @@ class ModelBase(object):
     def data(self, **options):
         """Called to serialize object to a dictionary."""
         data_fields = self._data_fields + self._auto_generated_attrs
-        return dict([(field, self[field]) for field in data_fields])
+        return {field: self[field] for field in data_fields}
 
     def is_valid(self):
         """Called when persisting data to ensure the format is correct."""
@@ -84,8 +84,7 @@ class RemoteModelBase(ModelBase):
 
     def _data_item(self, data_object):
         data_fields = self._data_fields + self._auto_generated_attrs
-        return dict([(field, getattr(data_object, field))
+        return {field: getattr(data_object, field) for field in data_fields}
-                     for field in data_fields])
 
     # data magic that will allow for a list of _data_object or a single item
     # if the object is a list, it will turn it into a list of hash's again

trove/common/utils.py

@@ -69,14 +69,14 @@ def create_method_args_string(*args, **kwargs):
 def stringify_keys(dictionary):
     if dictionary is None:
         return None
-    return dict((str(key), value) for key, value in dictionary.iteritems())
+    return {str(key): value for key, value in dictionary.iteritems()}
 
 
 def exclude(key_values, *exclude_keys):
     if key_values is None:
         return None
-    return dict((key, value) for key, value in key_values.iteritems()
+    return {key: value for key, value in key_values.iteritems()
-                if key not in exclude_keys)
+            if key not in exclude_keys}
 
 
 def generate_uuid():

trove/common/wsgi.py

@@ -409,8 +409,8 @@ class Controller(object):
             self.exception_map)
 
     def _extract_limits(self, params):
-        return dict([(key, params[key]) for key in params.keys()
+        return {key: params[key] for key in params.keys()
-                     if key in ["limit", "marker"]])
+                if key in ["limit", "marker"]}
 
 
 class TroveResponseSerializer(base_wsgi.ResponseSerializer):
@@ -513,8 +513,8 @@ class ContextMiddleware(base_wsgi.Middleware):
         super(ContextMiddleware, self).__init__(application)
 
     def _extract_limits(self, params):
-        return dict([(key, params[key]) for key in params.keys()
+        return {key: params[key] for key in params.keys()
-                     if key in ["limit", "marker"]])
+                if key in ["limit", "marker"]}
 
     def process_request(self, request):
         service_catalog = None

trove/extensions/security_group/service.py

@@ -39,7 +39,7 @@ class SecurityGroupController(wsgi.Controller):
                                                      deleted=False)
 
         # Construct the mapping from Security Groups to Security Group Rules
-        rules_map = dict([(g.id, g.get_rules()) for g in sec_groups])
+        rules_map = {g.id: g.get_rules() for g in sec_groups}
 
         return wsgi.Result(
             views.SecurityGroupsView(sec_groups,

trove/limits/service.py

@@ -28,7 +28,7 @@ class LimitsController(wsgi.Controller):
         Return all absolute and rate limit information.
         """
         quotas = QUOTAS.get_all_quotas_by_tenant(tenant_id)
-        abs_limits = dict((k, v['hard_limit']) for k, v in quotas.items())
+        abs_limits = {k: v['hard_limit'] for k, v in quotas.items()}
         rate_limits = req.environ.get("trove.limits", [])
 
         return wsgi.Result(views.LimitViews(abs_limits,

trove/quota/quota.py

@@ -58,9 +58,8 @@ class DbQuotaDriver(object):
         """
 
         all_quotas = Quota.find_all(tenant_id=tenant_id).all()
-        result_quotas = dict((quota.resource, quota)
+        result_quotas = {quota.resource: quota for quota in all_quotas
-                             for quota in all_quotas
+                         if quota.resource in resources}
-                             if quota.resource in resources)
 
         if len(result_quotas) != len(resources):
             for resource in resources:
@@ -94,9 +93,8 @@ class DbQuotaDriver(object):
         """
 
         all_usages = QuotaUsage.find_all(tenant_id=tenant_id).all()
-        result_usages = dict((usage.resource, usage)
+        result_usages = {usage.resource: usage for usage in all_usages
-                             for usage in all_usages
+                         if usage.resource in resources}
-                             if usage.resource in resources)
         if len(result_usages) != len(resources):
             for resource in resources:
                 # Not in the DB, return default value