A recursive subclass of ChainMap
Project description
DeepChainMap
A recursive subclass of the builtin Python class collections.ChainMap
.
Installation
pip install deep-chainmap
Usage
The canonical use case for the builtin class collections.ChainMap
is to
aggregate configuration data from layered mapping (basically dictionaries)
sources. However, it is not suited for non-flat (nested) mappings, the lookup
mechanism only works for the top level of a mapping.
deep_chainmap.DeepChainMap
provides a simple solution to this problem by making
recurive lookups in arbitrarily deeply nested mappings. Let's illustrate this
with a simple example. We will simulate 3 layers of mapping, and pretend they
were obtained from different sources (a default configuration, a configuration
file and the command line).
from deep_chainmap import DeepChainMap
default_layer = {
"architecture": "gpu",
"logging_level": "warning",
"solver": "RK4",
"database": {
"url": "unset",
"keep_in_sync": False,
},
"mesh": {
"type": "rectangular",
"resolution": {
"x": {
"npoints": 100,
"spacing": "linear",
},
"y": {
"npoints": 100,
"spacing": "linear",
},
"z": {
"npoints": 100,
"spacing": "linear",
},
},
},
}
config_file_layer = {
"architecture": "cpu",
"mesh": {
"resolution": {
"x": {
"spacing": "log",
},
"z": {
"npoints": 1,
},
},
},
}
cli_layer = {
"logging_level": "debug",
"database": {
"url": "https://my.database.api",
"keep_in_sync": True
},
}
# now building a DeepChainMap
cm = DeepChainMap(cli_layer, config_file_layer, default_layer)
Now when a single parameter is requested, it is looked up in each layer until a
value is found, by order of insertion (here the cli_layer
takes priority).
>>> cm["logging_level"]
'debug'
>>> cm["mesh"]["resolution"]["x"]["spacing"]
'log'
>>> cm["mesh"]["resolution"]["x"]["npoints"]
100
It is possible to produce a flat view of a DeepChainMap
instance as a builtin dict
:
>>> cm.flatten()
{
'architecture': 'cpu',
'logging_level': 'debug',
'solver': 'RK4',
'database': {
'url': 'https://my.database.api',
'keep_in_sync': True
},
'mesh': {
'type': 'rectangular',
'resolution': {
'x': {'npoints': 100, 'spacing': 'log'},
'y': {'npoints': 100, 'spacing': 'linear'},
'z': {'npoints': 1, 'spacing': 'linear'}
}
}
}
Additionally, each submapping from any level can be retrieved as a new layered-mapping
>>> cm["mesh"]
DeepChainMap({'resolution': {'x': {'spacing': 'log'}, 'z': {'npoints': 1}}},
{'resolution': {'x': {'npoints': 100, 'spacing': 'linear'},
'y': {'npoints': 100, 'spacing': 'linear'},
'z': {'npoints': 100, 'spacing': 'linear'}},
'type': 'rectangular'})
Which implies that they can be flatten as well
>>> cm["mesh"].flatten()
{
'type': 'rectangular',
'resolution': {
'x': {'npoints': 100, 'spacing': 'log'},
'y': {'npoints': 100, 'spacing': 'linear'},
'z': {'npoints': 1, 'spacing': 'linear'}
}
}
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