openstack/nova
Code Issues Proposed changes

Performance: leverage dict comprehension in PEP-0274

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PEP-0274 introduced dict comprehensions to replace dict constructor
with a sequence of length-2 sequences, 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.
Nova dropped python 2.6 support, we can leverage this now.
There is deep dive about PEP-0274[2] and basic tests about
performance[3].
Note: This commit doesn't handle dict constructor with kwagrs.
This commit also adds a hacking rule.

[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: Ifb5cb05b9cc2b8758d5a8e34f7792470a73d7c40
This commit is contained in:
ChangBo Guo(gcb)
2014-12-24 18:10:30 +08:00
parent a9fca62914
commit 69fef14509
54 changed files with 170 additions and 143 deletions
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12
nova/block_device.py
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@@ -86,9 +86,7 @@ class BlockDeviceDict(dict):
if bdm_dict.get('device_name'):
bdm_dict['device_name'] = prepend_dev(bdm_dict['device_name'])
# NOTE (ndipanov): Never default db fields
self.update(
dict((field, None)
for field in self._fields - do_not_default))
self.update({field: None for field in self._fields - do_not_default})
self.update(list(bdm_dict.iteritems()))
def _validate(self, bdm_dict):
@@ -139,8 +137,8 @@ class BlockDeviceDict(dict):
non_computable_fields = set(['boot_index', 'disk_bus',
'guest_format', 'device_type'])
new_bdm = dict((fld, val) for fld, val in legacy_bdm.iteritems()
if fld in copy_over_fields)
new_bdm = {fld: val for fld, val in legacy_bdm.iteritems()
if fld in copy_over_fields}
virt_name = legacy_bdm.get('virtual_name')
@@ -203,8 +201,8 @@ class BlockDeviceDict(dict):
copy_over_fields |= (bdm_db_only_fields |
bdm_db_inherited_fields)
legacy_block_device = dict((field, self.get(field))
for field in copy_over_fields if field in self)
legacy_block_device = {field: self.get(field)
for field in copy_over_fields if field in self}
source_type = self.get('source_type')
destination_type = self.get('destination_type')