Configuration

As shown in Concepts and usage, a Computer can be populated programmatically. genno can also read a simple configuration format in which settings and tasks are specified.

Overview

Ways to configure

Configuration is read through the Computer.configure() method, or the top level genno.configure() function.

Both methods accept either keyword arguments specifying the configuration values, or a path keyword argument that gives the path to a .json or .yaml-format file. For instance, the following are all equivalent:

# Create the computer before configuring from a JSON file
c = Computer()
c.configure(path="config-W.json")

# Create and configure from a YAML file in one step
c = Computer(path="config-W.yaml")

# Pass a data structure to configure()
info = dict(
  general=[
    dict(comp="product", key="W:a-b-c-d", inputs=["X::", "Y:d"], sums=True)
  ]
)
c = Computer()
c.configure(**info)

# Use the API to add a computation directly
c = Computer()
# add_product() infers the dimensions of W will be a-b-c-d
c.add_product("W", "X:a-b-c-d", "Y:d", sums=True)

…with the following file contents:

config-W.yaml
general:
- comp: product
  key: W:a-b-c-d
  inputs: ["X::", "Y:d"]
  sums: true
config-W.json
{
  "general": [
    {
      "comp": "product",
      "key": "W:a-b-c-d",
      "inputs": ["X::", "Y:d"],
      "sums": true
    }
  ]
}

Global- and specific configuration

Configuration is either global or specific to a certain Computer. For instance, units: configuration is global; it affects all Computers, and can be set using either genno.configure() or Computer.configure() On the other hand, other configuration such as files: input adds specific tasks to a Computer, so it can only be used with Computer.configure().

genno.configure(path=None, **config)

Configure genno globally.

Modifies global variables that affect the behaviour of all Computers and computations.

Warns

UserWarning – If config contains unrecognized keys.

Custom handlers

The configuration file is divided into sections. Generally each section contains a list of items, and each item is itself a mapping; see the built-in sections listed below. genno.config has one handler function for each section, and is extensible. For instance, the genno compatibility modules for ixmp and pyam define handlers for sections rename_dims: and iamc:, respectively.

The handles() decorator can be used to mark a custom function that handles a custom configuration section:

from genno.config import handles

@handles("my-section")
def custom_handler(c: Computer, info):
    print(f"Handle {info['name']}")
    print(f"  with inputs {repr(info['inputs'])}")

    # Use a default value for one setting
    key = info.get("key", "foo")
    print(f"Output key: {key}")

    # Manipulate the Computer instance `c` in some way
    c.add("… etc.")
my-config.yaml
 # This section is handled by genno's built-in handlers
 general:
 - comp: product
    key: W:a-b-c-d
    inputs: ["X::", "Y:d"]
    sums: true

 # These items are handled by the custom handler
 my-section:
 - name: item-a
   inputs: [X, Y]
 - name: item-b
   key: bar
   inputs: [W, Z]
genno.config.handles(section_name, type_=<class 'list'>, keep=False, apply=True)

Decorator for a configuration section handler.

Specific sections

aggregate:

genno.config.aggregate(c: genno.core.computer.Computer, info)

Handle one entry from the aggregate: config section.

Computer-specific configuration.

Invokes Computer.aggregate() add tasks with computations.aggregate() or computations.sum(), computing sums across labels within one dimension of a quantity. Each entry contains:

  • _quantities: list of 0 or more keys of Quantities to be aggregated. The full dimensionality of the key(s) is inferred.

  • _tag (str): new tag to append to the keys for the aggregated quantities.

  • _dim (str): dimensions on which to aggregate.

All other keys are treated as group names; the corresponding values are lists of labels along the dimension to sum.

Example:

aggregate:
- _quantities: [foo, bar]
  _tag: aggregated
  _dim: a

  baz123: [baz1, baz2, baz3]
  baz12: [baz1, baz2]

If the full dimensionality of the input quantities are foo:a-b and bar:a-b-c, then add_aggregate() creates the new quantities foo:a-b:aggregated and bar:a-b-c:aggregated. These new quantities have the new labels baz123 and baz12 along their a dimension, with sums of the indicated values.

alias:

genno.config.alias(c: genno.core.computer.Computer, info)

Handle one entry from the alias: config section.

Computer-specific configuration.

This section simply makes the output of one task available under another key.

alias:
  "foo:x-y": "bar:x-y"
  "baz:x-y": "bar:x-y"

combine:

genno.config.combine(c: genno.core.computer.Computer, info)

Handle one entry from the combine: config section.

Computer-specific configuration.

Invokes Computer.add_combination() to add tasks with computations.combine(), computing a weighted sum of multiple Quantities. Each item contains:

  • key: key for the new quantity, including dimensionality.

  • inputs: a list of dicts specifying inputs to the weighted sum. Each dict contains:

    • quantity (required): key for the input quantity. add_combination() infers the proper dimensionality from the dimensions of key plus dimension to select on.

    • select (dict, optional): selectors to be applied to the input quantity. Keys are dimensions; values are either single labels, or lists of labels. In the latter case, the sum is taken across these values, so that the result has the same dimensionality as key.

    • weight (int, optional): weight for the input quantity; default 1.

Example. For the following YAML:

combine:
- key: foo:a-b-c
  inputs:
  - quantity: bar
    weight: -1
  - quantity: baz::tag
    select: {d: [d1, d2, d3]}

…add_combination() infers:

\[\text{foo}_{abc} = -1 \times \text{bar}_{abc} + 1 \times \sum_{d \in \{ d1, d2, d3 \}}{\text{baz}_{abcd}^\text{(tag)}} \quad \forall \quad a, b, c\]

default: key/task

genno.config.default(c: genno.core.computer.Computer, info)

Handle the default: config section.

Computer-specific configuration.

This sets Computer.default_key, used when get() is called without arguments.

files: input

genno.config.files(c: genno.core.computer.Computer, info)

Handle one entry from the files: config section.

Computer-specific configuration.

Invokes Computer.add_file() to add computations.load_file(). If the path key is a relative path, it is resolved relative to the directory that contains the configuration file, else the current working directory.

files:
- path: ./input0.csv
  key: d_check
# 'dims' argument can be supplied as list or dict
- path: ./input1.csv
  key: input1-0
  dims: [i, j_dim]  # Omit extra dimension 'foo'
- path: ./input1.csv
  key: input1-1
  dims: {i: i, j_dim: j}

general:

genno.config.general(c: genno.core.computer.Computer, info)

Handle one entry from the general: config section.

Computer-specific configuration.

This is, as the name implies, the most generalized section. Each item contains:

  • comp: this refers to the name of a computation that is available in the namespace of genno.computations, or custom computations registered by compatibility modules or third-party packages. E.g. if “product”, then Computer.add_product() is called, which also automatically infers the correct dimensions for each input.

  • key: the key for the computed quantity.

  • inputs: a list of keys to which the computation is applied.

  • args (dict, optional): keyword arguments to the computation.

  • add args (dict, optional): keyword arguments to Computer.add() itself.

report:

genno.config.report(c: genno.core.computer.Computer, info)

Handle one entry from the report: config section.

Computer-specific configuration.

A ‘report’ is a concatenation of 1 or more other quantities. Example:

report:
- key: foo
  members: [X, Y]

units:

genno.config.units(c: genno.core.computer.Computer, info)

Handle the units: config section.

Global configuration.

Sub-keys:

units:
  replace:
    dollar: USD
  # YAML multi-line string
  define: |-
    pp = [person]
    tiny = 0.1 millimetre