calculation_state.py

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#!/usr/bin/env python
from flexbe_core import EventState, Logger


class CalculationState(EventState):
    '''
    Implements a state that can perform a calculation based on userdata.
    calculation is a function which takes exactly one parameter, input_value from userdata,
    and its return value is stored in output_value after leaving the state.

    -- calculation  function    The function that performs the desired calculation.
                                It could be a private function (self.foo) manually defined in a behavior's source code
                                or a lambda function (e.g., lambda x: x^2, where x will be the input_value).

    ># input_value  object              Input to the calculation function.

    #> output_value object              The result of the calculation.

    <= done                                             Indicates completion of the calculation.
    '''

    def __init__(self, calculation):
        super(CalculationState, self).__init__(outcomes=['done'],
                                               input_keys=['input_value'],
                                               output_keys=['output_value'])
        self._calculation = calculation
        self._calculation_result = None

    def execute(self, userdata):
        userdata.output_value = self._calculation_result
        # nothing to check
        return 'done'

    def on_enter(self, userdata):
        if self._calculation is not None:
            try:
                self._calculation_result = self._calculation(userdata.input_value)
            except Exception as e:
                Logger.logwarn('Failed to execute calculation function!\n%s' % str(e))
        else:
            Logger.logwarn('Passed no calculation!')