[Notes] [Git][BuildStream/buildstream][danielsilverstone-ct/improve-chainmap-get] _yaml.py: Implement `get()` for `ChainMap`

[Daniel Silverstone <gitlab mg gitlab com>]

Title: GitLab

Daniel Silverstone pushed to branch danielsilverstone-ct/improve-chainmap-get at BuildStream / buildstream

Commits:

• d868b409
  by Daniel Silverstone at 2018-11-01T13:40:24Z

  _yaml.py: Implement `get()` for `ChainMap`
  
  Since the core Python `ChainMap.get()` implements with:
  
      self[key] if key in self else default
  
  The double-chain-lookup is expensive.  This simple change solves that
  for our ChainMap derived structure.  As such it improves matters
  for #466 somewhat.
  
  Signed-off-by: Daniel Silverstone <daniel silverstone codethink co uk>
  

1 changed file:

• buildstream/_yaml.py

Changes:

buildstream/_yaml.py

---

...	...	@@ -1049,6 +1049,12 @@ class ChainMap(collections.ChainMap):
1049	1049	for key in clearable:
1050	1050	del self[key]
1051	1051
	1052	+ def get(self, key, default=None):
	1053	+ try:
	1054	+ return self[key]
	1055	+ except KeyError:
	1056	+ return default
	1057	+
1052	1058
1053	1059	def node_chain_copy(source):
1054	1060	copy = ChainMap({}, source)

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