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from __future__ import ( |
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absolute_import, |
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division, |
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print_function |
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) |
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import abc |
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import json |
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import logging |
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import jinja2 |
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import jinja2.meta |
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from .state_status import StepStateStatus |
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from .step_results import ( |
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ActivityStepResult, |
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TemplatedStepResult, |
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) |
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_LOGGER = logging.getLogger(__name__) |
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class StepError(StandardError): |
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pass |
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class StepDefinitionError(StepError): |
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pass |
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class Step(object): |
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"""Base `Step` in a workflow. |
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A `Step` is composed of a name and a collection of its requirements. |
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""" |
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__slots__ = ('name', 'requires') |
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__metaclass__ = abc.ABCMeta |
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def __init__(self, name, requires=()): |
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self.name = name |
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self.requires = dict([self._resolve_parent(parent_def) |
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for parent_def in requires]) |
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@staticmethod |
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def _resolve_parent(parent_def): |
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if isinstance(parent_def, basestring): |
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return (parent_def, StepStateStatus.completed) |
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else: |
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try: |
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parent_name, status_name = parent_def |
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return (parent_name, getattr(StepStateStatus, status_name)) |
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except AttributeError as err: |
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raise StepDefinitionError('Invalid Step status name: %r' % |
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err.args[0]) |
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except StandardError: |
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raise StepDefinitionError('Invalid Step definition: %r' % |
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parent_def) |
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@classmethod |
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def from_data(cls, step_data, activities): |
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"""Create a new Step object from a step definition""" |
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# FIXME: pass data through JSONSchema |
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if 'activity' in step_data: |
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activity_name = step_data['activity'] |
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activity = activities[activity_name] |
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step = ActivityStep( |
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name=step_data['name'], |
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requires=step_data.get('requires', ()), |
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activity=activity, |
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input_template=step_data.get('input', None), |
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) |
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elif 'eval' in step_data: |
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step = TemplatedStep( |
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name=step_data['name'], |
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requires=step_data.get('requires', ()), |
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eval_block=step_data['eval'], |
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) |
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else: |
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raise ValueError('Invalid Step data: %r' % step_data) |
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return step |
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@abc.abstractmethod |
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def prepare(self, _context): |
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"""Prepare step's input from context. |
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:returns: |
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Step's input |
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""" |
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pass |
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@abc.abstractmethod |
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def run(self, _step_input): |
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"""Run the step from its input. |
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:returns: |
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A StepResult object |
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""" |
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pass |
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@abc.abstractmethod |
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def render(self, _output): |
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"""Renders the Step's output for usage by other steps. |
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:returns: |
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A dictionary of 'key: value' pairs. |
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""" |
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pass |
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def __repr__(self): |
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return '{ctype}(name={name})'.format(ctype=self.__class__.__name__, |
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name=self.name) |
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class ActivityStep(Step): |
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__slots__ = ('activity', 'input_template', '__env') |
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def __init__(self, name, activity, input_template, requires=()): |
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super(ActivityStep, self).__init__(name, requires) |
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self.activity = activity |
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self.input_template = None |
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# Define the Jinga2 environment |
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self.__env = jinja2.Environment(finalize=self.__jsonify) |
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if input_template is not None: |
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tp_required = self._check_template_dependencies(input_template) |
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for tp_var in tp_required: |
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# `__input__` is a "magic" step referencing the workflow input |
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if tp_var == '__input__': |
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continue |
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if tp_var not in self.requires: |
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raise StepDefinitionError( |
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'Invalid step %r: Template used %r is not required' % |
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(self.name, tp_var,) |
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) |
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self.input_template = self.__env.from_string(input_template) |
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def __jsonify(self, obj): |
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# Note: This method is called by Jinja2 to "finalize" its variables. |
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# Jinja2 also calls it to "finalize" the non-variable chunks |
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# of a template's string when compiling the template, so we have |
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# to be careful of extra quoting. |
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if self.input_template is not None: |
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# Now that the templates are defined, we can define the "finalize" |
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# function to JSON dump all template variables. |
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return json.dumps(obj, indent=4, sort_keys=True) |
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else: |
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return obj |
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def prepare(self, context): |
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if self.input_template is not None: |
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activity_input_json = self.input_template.render(context) |
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# FIXME: We are assuming JSON activity input here |
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try: |
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activity_input = json.loads(activity_input_json) |
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except ValueError: |
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_LOGGER.exception('Invalid template result: %r', |
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activity_input_json) |
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raise |
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else: |
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activity_input = None |
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self.activity.check_input(activity_input) |
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return activity_input |
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def run(self, step_input): |
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return ActivityStepResult( |
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name=self.name, |
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activity=self.activity, |
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activity_input=step_input, |
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) |
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def render(self, output): |
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return self.activity.render_outputs(output) |
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def _check_template_dependencies(self, input_template): |
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"""Return the list of used external variable in the template. |
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""" |
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parsed_template = self.__env.parse(input_template) |
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return jinja2.meta.find_undeclared_variables(parsed_template) |
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class TemplatedStep(Step): |
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__slots__ = ('eval_block') |
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def __init__(self, name, eval_block, requires=()): |
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super(TemplatedStep, self).__init__(name, requires) |
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self.eval_block = jinja2.Template(eval_block) |
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def prepare(self, context): |
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return self.eval_block.render(context) |
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def run(self, _step_input): |
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return TemplatedStepResult() |
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def render(self, _output): |
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# NOTE: Templated steps do not have any usable attributes |
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return {} |
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The coding style of this project requires that you add a docstring to this code element. Below, you find an example for methods:
If you would like to know more about docstrings, we recommend to read PEP-257: Docstring Conventions.