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Parameters

Parsing prefix keywords

There is 2 allowed parsing prefix keywords:

  • input: corresponding to the input_data.
  • output : corresponding to the result output data (returned by the apply_rules() method).

Here are examples:

  1. input.name: maps to input_data["name"].
  2. output.check_admission.is_admitted: maps to result["check_admission"]["is_admitted"].

They both can be used in condition and action parameters.

Info

A value without any prefix keyword is a constant.

Parsing error

Raise by default

By default, errors during condition and action parameters parsing are raised.

If we refer to the dictionary example:

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rules = {
    "check_admission": {
        "ADMITTED_RULE": {
            "condition": lambda power: power in ["strength", "fly", "immortality"],
            "condition_parameters": {"power": "input.super_power"}, 
            "action": set_admission,
            "action_parameters": {"value": True},
        },
        "DEFAULT_RULE": {
            "condition": None,
            "condition_parameters": None, 
            "action": set_admission,
            "action_parameters": {"value": False},
        },
    }
}

With modified data like:

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input_data = {
    "id": 1,
    "name": "Superman",
    "civilian_name": "Clark Kent",
    "age": None,
    "city": "Metropolis",
    "language": "french",
    "power": "fly",
    "favorite_meal": "Spinach",
    "secret_weakness": "Kryptonite",
    "weapons": [],
}

By default we will get a KeyError exception during the execution of the apply_rules() method because of power vs super_power.

Ignore

You can change the by default raising behavior of the parameter's parsing.

Two ways are possible:

  • At the configuration level: impacts all the parameters.
  • At the parameter's level.

Configuration level

You just have to add the following key somewhere in your configuration:

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---
rules:
  default_rule_set:
    check_admission:
      ADMITTED_RULE:
        condition: HAS_SCHOOL_AUTHORIZED_POWER
        action: set_admission
        action_parameters:
          value: true
      DEFAULT_RULE:
        condition: null
        action: set_admission
        action_parameters:
          value: false

conditions:
  HAS_SCHOOL_AUTHORIZED_POWER:
    description: "Does applicant have a school authorized power?"
    validation_function: has_authorized_super_power
    condition_parameters:
      power: input.super_power

conditions_source_modules:
  - my_folder.conditions
actions_source_modules: 
  - my_folder.actions

parsing_error_strategy: ignore  # (1)
  1. parsing_error_strategy has two possible values: raise and ignore.

It will affect all the parameters.

Parameter level

Quick Sum Up

  • input.super_power?: set the value to None
  • input.super_power?no_power: set the value to no_power
  • input.super_power!: force raise exception (case when ignore is set by default)

You can also handle more precisely that aspect at parameter's level:

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---
rules:
  default_rule_set:
    check_admission:
      ADMITTED_RULE:
        condition: HAS_SCHOOL_AUTHORIZED_POWER
        action: set_admission
        action_parameters:
          value: true
      DEFAULT_RULE:
        condition: null
        action: set_admission
        action_parameters:
          value: false

conditions:
  HAS_SCHOOL_AUTHORIZED_POWER:
    description: "Does applicant have a school authorized power?"
    validation_function: has_authorized_super_power
    condition_parameters:
      power: input.super_power?  # (1)

conditions_source_modules:
  - my_folder.conditions
actions_source_modules: 
  - my_folder.actions
  1. Have you noticed the '?' ? If there is a KeyError when reading, power will be set to None rather than raising the exception.

Info

You can enforce raising exceptions at parameter's level with !.

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power: input.super_power!

Default value (parameter level)

Finally, you can set a default value at parameter's level. This value will be used if there is an exception during parsing:

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---
rules:
  default_rule_set:
    check_admission:
      ADMITTED_RULE:
        condition: HAS_SCHOOL_AUTHORIZED_POWER
        action: set_admission
        action_parameters:
          value: true
      DEFAULT_RULE:
        condition: null
        action: set_admission
        action_parameters:
          value: false

conditions:
  HAS_SCHOOL_AUTHORIZED_POWER:
    description: "Does applicant have a school authorized power?"
    validation_function: has_authorized_super_power
    condition_parameters:
      power: input.super_power?no_power  # (1)

conditions_source_modules:
  - my_folder.conditions
actions_source_modules: 
  - my_folder.actions
  1. If there is an exception during parsing, power will be set to "no_power".

Good to know

Parameter's level is overriding configuration level.