Prefect

Released April 4, 2019

Features

- API reference documentation is now versioned - [270](https://github.com/PrefectHQ/prefect/issues/270)
- Add `S3ResultHandler` for handling results to / from S3 buckets - [879](https://github.com/PrefectHQ/prefect/pull/879)
- Add ability to use `Cached` states across flow runs in Cloud - [885](https://github.com/PrefectHQ/prefect/pull/885)

Enhancements
- Bump to latest version of `pytest` (4.3) - [814](https://github.com/PrefectHQ/prefect/issues/814)
- `Client.deploy` accepts optional `build` kwarg for avoiding building Flow environment - [876](https://github.com/PrefectHQ/prefect/pull/876)
- Bump `distributed` to 1.26.1 for enhanced security features - [878](https://github.com/PrefectHQ/prefect/pull/878)
- Local secrets automatically attempt to load secrets as JSON - [883](https://github.com/PrefectHQ/prefect/pull/883)
- Add task logger to context for easily creating custom logs during task runs - [884](https://github.com/PrefectHQ/prefect/issues/884)

Task Library

- Add `ParseRSSFeed` for parsing a remote RSS feed - [856](https://github.com/PrefectHQ/prefect/pull/856)
- Add tasks for working with Docker containers and imaged - [864](https://github.com/PrefectHQ/prefect/pull/864)
- Add task for creating a BigQuery table - [895](https://github.com/PrefectHQ/prefect/pull/895)

Fixes

- Only checkpoint tasks if running in cloud - [839](https://github.com/PrefectHQ/prefect/pull/839), [#854](https://github.com/PrefectHQ/prefect/pull/854)
- Adjusted small flake8 issues for names, imports, and comparisons - [849](https://github.com/PrefectHQ/prefect/pull/849)
- Fix bug preventing `flow.run` from properly using cached tasks - [861](https://github.com/PrefectHQ/prefect/pull/861)
- Fix tempfile usage in `flow.visualize` so that it runs on Windows machines - [858](https://github.com/PrefectHQ/prefect/issues/858)
- Fix issue caused by Python 3.5.2 bug for Python 3.5.2 compatibility - [857](https://github.com/PrefectHQ/prefect/issues/857)
- Fix issue in which `GCSResultHandler` was not pickleable - [879](https://github.com/PrefectHQ/prefect/pull/879)
- Fix issue with automatically converting callables and dicts to tasks - [894](https://github.com/PrefectHQ/prefect/issues/894)

Breaking Changes

- Change the call signature of `Dict` task from `run(**task_results)` to `run(keys, values)` - [894](https://github.com/PrefectHQ/prefect/issues/894)

Contributors

- [ColCarroll](https://github.com/ColCarroll)
- [dhirschfeld](https://github.com/dhirschfeld)
- [BasPH](https://github.com/BasPH)
- [Miloš Garunović](https://github.com/milosgarunovic)
- [Nash Taylor](https://github.com/ntaylorwss)

Released March 24, 2019

Features

- Add `checkpoint` option for individual `Task`s, as well as a global `checkpoint` config setting for storing the results of Tasks using their result handlers - [649](https://github.com/PrefectHQ/prefect/pull/649)
- Add `defaults_from_attrs` decorator to easily construct `Task`s whose attributes serve as defaults for `Task.run` - [293](https://github.com/PrefectHQ/prefect/issues/293)
- Environments follow new hierarchy (PIN-3) - [670](https://github.com/PrefectHQ/prefect/pull/670)
- Add `OneTimeSchedule` for one-time execution at a specified time - [680](https://github.com/PrefectHQ/prefect/pull/680)
- `flow.run` is now a blocking call which will run the Flow, on its schedule, and execute full state-based execution (including retries) - [690](https://github.com/PrefectHQ/prefect/issues/690)
- Pre-populate `prefect.context` with various formatted date strings during execution - [704](https://github.com/PrefectHQ/prefect/pull/704)
- Add ability to overwrite task attributes such as "name" when calling tasks in the functional API - [717](https://github.com/PrefectHQ/prefect/issues/717)
- Release Prefect Core under the Apache 2.0 license - [762](https://github.com/PrefectHQ/prefect/pull/762)

Enhancements

- Refactor all `State` objects to store fully hydrated `Result` objects which track information about how results should be handled - [612](https://github.com/PrefectHQ/prefect/pull/612), [#616](https://github.com/PrefectHQ/prefect/pull/616)
- Add `google.cloud.storage` as an optional extra requirement so that the `GCSResultHandler` can be exposed better - [626](https://github.com/PrefectHQ/prefect/pull/626)
- Add a `start_time` check for Scheduled flow runs, similar to the one for Task runs - [605](https://github.com/PrefectHQ/prefect/issues/605)
- Project names can now be specified for deployments instead of IDs - [633](https://github.com/PrefectHQ/prefect/pull/633)
- Add a `createProject` mutation function to the client - [633](https://github.com/PrefectHQ/prefect/pull/633)
- Add timestamp to auto-generated API docs footer - [639](https://github.com/PrefectHQ/prefect/pull/639)
- Refactor `Result` interface into `Result` and `SafeResult` - [649](https://github.com/PrefectHQ/prefect/pull/649)
- The `manual_only` trigger will pass if `resume=True` is found in context, which indicates that a `Resume` state was passed - [664](https://github.com/PrefectHQ/prefect/issues/664)
- Added DockerOnKubernetes environment (PIN-3) - [670](https://github.com/PrefectHQ/prefect/pull/670)
- Added Prefect docker image (PIN-3) - [670](https://github.com/PrefectHQ/prefect/pull/670)
- `defaults_from_attrs` now accepts a splatted list of arguments - [676](https://github.com/PrefectHQ/prefect/issues/676)
- Add retry functionality to `flow.run(on_schedule=True)` for local execution - [680](https://github.com/PrefectHQ/prefect/pull/680)
- Add `helper_fns` keyword to `ShellTask` for pre-populating helper functions to commands - [681](https://github.com/PrefectHQ/prefect/pull/681)
- Convert a few DEBUG level logs to INFO level logs - [682](https://github.com/PrefectHQ/prefect/issues/682)
- Added DaskOnKubernetes environment (PIN-3) - [695](https://github.com/PrefectHQ/prefect/pull/695)
- Load `context` from Cloud when running flows - [699](https://github.com/PrefectHQ/prefect/pull/699)
- Add `Queued` state - [705](https://github.com/PrefectHQ/prefect/issues/705)
- `flow.serialize()` will always serialize its environment, regardless of `build` - [696](https://github.com/PrefectHQ/prefect/issues/696)
- `flow.deploy()` now raises an informative error if your container cannot deserialize the Flow - [711](https://github.com/PrefectHQ/prefect/issues/711)
- Add `_MetaState` as a parent class for states that modify other states - [726](https://github.com/PrefectHQ/prefect/pull/726)
- Add `flow` keyword argument to `Task.set_upstream()` and `Task.set_downstream()` - [749](https://github.com/PrefectHQ/prefect/pull/749)
- Add `is_retrying()` helper method to all `State` objects - [753](https://github.com/PrefectHQ/prefect/pull/753)
- Allow for state handlers which return `None` - [753](https://github.com/PrefectHQ/prefect/pull/753)
- Add daylight saving time support for `CronSchedule` - [729](https://github.com/PrefectHQ/prefect/pull/729)
- Add `idempotency_key` and `context` arguments to `Client.create_flow_run` - [757](https://github.com/PrefectHQ/prefect/issues/757)
- Make `EmailTask` more secure by pulling credentials from secrets - [706](https://github.com/PrefectHQ/prefect/issues/706)

Task Library

- Add `GCSUpload` and `GCSDownload` for uploading / retrieving string data to / from Google Cloud Storage - [673](https://github.com/PrefectHQ/prefect/pull/673)
- Add `BigQueryTask` and `BigQueryInsertTask` for executing queries against BigQuery tables and inserting data - [678](https://github.com/PrefectHQ/prefect/pull/678), [#685](https://github.com/PrefectHQ/prefect/pull/685)
- Add `FilterTask` for filtering out lists of results - [637](https://github.com/PrefectHQ/prefect/issues/637)
- Add `S3Download` and `S3Upload` for interacting with data stored on AWS S3 - [692](https://github.com/PrefectHQ/prefect/issues/692)
- Add `AirflowTask` and `AirflowTriggerDAG` tasks to the task library for running individual Airflow tasks / DAGs - [735](https://github.com/PrefectHQ/prefect/issues/735)
- Add `OpenGitHubIssue` and `CreateGitHubPR` tasks for interacting with GitHub repositories - [771](https://github.com/PrefectHQ/prefect/pull/771)
- Add Kubernetes tasks for deployments, jobs, pods, and services - [779](https://github.com/PrefectHQ/prefect/pull/779)
- Add Airtable tasks - [803](https://github.com/PrefectHQ/prefect/pull/803)
- Add Twitter tasks - [803](https://github.com/PrefectHQ/prefect/pull/803)
- Add `GetRepoInfo` for pulling GitHub repository information - [816](https://github.com/PrefectHQ/prefect/pull/816)

Fixes

- Fix edge case in doc generation in which some `Exception`s' call signature could not be inspected - [513](https://github.com/PrefectHQ/prefect/issues/513)
- Fix bug in which exceptions raised within flow runner state handlers could not be sent to Cloud - [628](https://github.com/PrefectHQ/prefect/pull/628)
- Fix issue wherein heartbeats were not being called on a fixed interval - [669](https://github.com/PrefectHQ/prefect/pull/669)
- Fix issue wherein code blocks inside of method docs couldn't use `**kwargs` - [658](https://github.com/PrefectHQ/prefect/issues/658)
- Fix bug in which Prefect-generated Keys for S3 buckets were not properly converted to strings - [698](https://github.com/PrefectHQ/prefect/pull/698)
- Fix next line after Docker Environment push/pull from overwriting progress bar - [702](https://github.com/PrefectHQ/prefect/pull/702)
- Fix issue with `JinjaTemplate` not being pickleable - [710](https://github.com/PrefectHQ/prefect/pull/710)
- Fix issue with creating secrets from JSON documents using the Core Client - [715](https://github.com/PrefectHQ/prefect/pull/715)
- Fix issue with deserialization of JSON secrets unnecessarily calling `json.loads` - [716](https://github.com/PrefectHQ/prefect/pull/716)
- Fix issue where `IntervalSchedules` didn't respect daylight saving time after serialization - [729](https://github.com/PrefectHQ/prefect/pull/729)

Breaking Changes

- Remove the `BokehRunner` and associated webapp - [609](https://github.com/PrefectHQ/prefect/issues/609)
- Rename `ResultHandler` methods from `serialize` / `deserialize` to `write` / `read` - [612](https://github.com/PrefectHQ/prefect/pull/612)
- Refactor all `State` objects to store fully hydrated `Result` objects which track information about how results should be handled - [612](https://github.com/PrefectHQ/prefect/pull/612), [#616](https://github.com/PrefectHQ/prefect/pull/616)
- `Client.create_flow_run` now returns a string instead of a `GraphQLResult` object to match the API of `deploy` - [630](https://github.com/PrefectHQ/prefect/pull/630)
- `flow.deploy` and `client.deploy` require a `project_name` instead of an ID - [633](https://github.com/PrefectHQ/prefect/pull/633)
- Upstream state results now take precedence for task inputs over `cached_inputs` - [591](https://github.com/PrefectHQ/prefect/issues/591)
- Rename `Match` task (used inside control flow) to `CompareValue` - [638](https://github.com/PrefectHQ/prefect/pull/638)
- `Client.graphql()` now returns a response with up to two keys (`data` and `errors`). Previously the `data` key was automatically selected - [642](https://github.com/PrefectHQ/prefect/pull/642)
- `ContainerEnvironment` was changed to `DockerEnvironment` - [670](https://github.com/PrefectHQ/prefect/pull/670)
- The environment `from_file` was moved to `utilities.environments` - [670](https://github.com/PrefectHQ/prefect/pull/670)
- Removed `start_tasks` argument from `FlowRunner.run()` and `check_upstream` argument from `TaskRunner.run()` - [672](https://github.com/PrefectHQ/prefect/pull/672)
- Remove support for Python 3.4 - [671](https://github.com/PrefectHQ/prefect/issues/671)
- `flow.run` is now a blocking call which will run the Flow, on its schedule, and execute full state-based execution (including retries) - [690](https://github.com/PrefectHQ/prefect/issues/690)
- Remove `make_return_failed_handler` as `flow.run` now returns all task states - [693](https://github.com/PrefectHQ/prefect/pull/693)
- Refactor Airflow migration tools into a single `AirflowTask` in the task library for running individual Airflow tasks - [735](https://github.com/PrefectHQ/prefect/issues/735)
- `name` is now required on all Flow objects - [732](https://github.com/PrefectHQ/prefect/pull/732)
- Separate installation "extras" packages into multiple, smaller extras - [739](https://github.com/PrefectHQ/prefect/issues/739)
- `Flow.parameters()` always returns a set of parameters - [756](https://github.com/PrefectHQ/prefect/pull/756)

Major Features

- Add ability to run scheduled flows locally via `on_schedule` kwarg in `flow.run()` - [519](https://github.com/PrefectHQ/prefect/issues/519)
- Allow tasks to specify their own result handlers, ensure inputs and outputs are stored only when necessary, and ensure no raw data is sent to the database - [587](https://github.com/PrefectHQ/prefect/pull/587)

Minor Features

- Allow for building `ContainerEnvironment`s locally without pushing to registry - [514](https://github.com/PrefectHQ/prefect/issues/514)
- Make mapping more robust when running children tasks multiple times - [541](https://github.com/PrefectHQ/prefect/pull/541)
- Always prefer `cached_inputs` over upstream states, if available - [546](https://github.com/PrefectHQ/prefect/pull/546)
- Add hooks to `FlowRunner.initialize_run()` for manipulating task states and contexts - [548](https://github.com/PrefectHQ/prefect/pull/548)
- Improve state-loading strategy for Prefect Cloud - [555](https://github.com/PrefectHQ/prefect/issues/555)
- Introduce `on_failure` kwarg to Tasks and Flows for user-friendly failure callbacks - [551](https://github.com/PrefectHQ/prefect/issues/551)
- Include `scheduled_start_time` in context for Flow runs - [524](https://github.com/PrefectHQ/prefect/issues/524)
- Add GitHub PR template - [542](https://github.com/PrefectHQ/prefect/pull/542)
- Allow flows to be deployed to Prefect Cloud without a project id - [571](https://github.com/PrefectHQ/prefect/pull/571)
- Introduce serialization schemas for ResultHandlers - [572](https://github.com/PrefectHQ/prefect/issues/572)
- Add new `metadata` attribute to States for managing user-generated results - [573](https://github.com/PrefectHQ/prefect/issues/573)
- Add new 'JSONResultHandler' for serializing small bits of data without external storage - [576](https://github.com/PrefectHQ/prefect/issues/576)
- Use `JSONResultHandler` for all Parameter caching - [590](https://github.com/PrefectHQ/prefect/pull/590)

Fixes

- Fixed `flow.deploy()` attempting to access a nonexistent string attribute - [503](https://github.com/PrefectHQ/prefect/pull/503)
- Ensure all logs make it to the logger service in deployment - [508](https://github.com/PrefectHQ/prefect/issues/508), [#552](https://github.com/PrefectHQ/prefect/issues/552)
- Fix a situation where `Paused` tasks would be treated as `Pending` and run - [535](https://github.com/PrefectHQ/prefect/pull/535)
- Ensure errors raised in state handlers are trapped appropriately in Cloud Runners - [554](https://github.com/PrefectHQ/prefect/pull/554)
- Ensure unexpected errors raised in FlowRunners are robustly handled - [568](https://github.com/PrefectHQ/prefect/pull/568)
- Fixed non-deterministic errors in mapping caused by clients resolving futures of other clients - [569](https://github.com/PrefectHQ/prefect/pull/569)
- Older versions of Prefect will now ignore fields added by newer versions when deserializing objects - [583](https://github.com/PrefectHQ/prefect/pull/583)
- Result handler failures now result in clear task run failures - [575](https://github.com/PrefectHQ/prefect/issues/575)
- Fix issue deserializing old states with empty metadata - [590](https://github.com/PrefectHQ/prefect/pull/590)
- Fix issue serializing `cached_inputs` - [594](https://github.com/PrefectHQ/prefect/pull/594)

Breaking Changes

- Move `prefect.client.result_handlers` to `prefect.engine.result_handlers` - [512](https://github.com/PrefectHQ/prefect/pull/512)
- Removed `inputs` kwarg from `TaskRunner.run()` - [546](https://github.com/PrefectHQ/prefect/pull/546)
- Moves the `start_task_ids` argument from `FlowRunner.run()` to `Environment.run()` - [544](https://github.com/PrefectHQ/prefect/issues/544), [#545](https://github.com/PrefectHQ/prefect/pull/545)
- Convert `timeout` kwarg from `timedelta` to `integer` - [540](https://github.com/PrefectHQ/prefect/issues/540)
- Remove `timeout` kwarg from `executor.wait` - [569](https://github.com/PrefectHQ/prefect/pull/569)
- Serialization of States will _ignore_ any result data that hasn't been processed - [581](https://github.com/PrefectHQ/prefect/pull/581)
- Removes `VersionedSchema` in favor of implicit versioning: serializers will ignore unknown fields and the `create_object` method is responsible for recreating missing ones - [583](https://github.com/PrefectHQ/prefect/pull/583)
- Convert and rename `CachedState` to a successful state named `Cached`, and also remove the superfluous `cached_result` attribute - [586](https://github.com/PrefectHQ/prefect/issues/586)

Major Features

- Add support for Prefect Cloud - [374](https://github.com/PrefectHQ/prefect/pull/374), [#406](https://github.com/PrefectHQ/prefect/pull/406), [#473](https://github.com/PrefectHQ/prefect/pull/473), [#491](https://github.com/PrefectHQ/prefect/pull/491)
- Add versioned serialization schemas for `Flow`, `Task`, `Parameter`, `Edge`, `State`, `Schedule`, and `Environment` objects - [310](https://github.com/PrefectHQ/prefect/pull/310), [#318](https://github.com/PrefectHQ/prefect/pull/318), [#319](https://github.com/PrefectHQ/prefect/pull/319), [#340](https://github.com/PrefectHQ/prefect/pull/340)
- Add ability to provide `ResultHandler`s for storing private result data - [391](https://github.com/PrefectHQ/prefect/pull/391), [#394](https://github.com/PrefectHQ/prefect/pull/394), [#430](https://github.com/PrefectHQ/prefect/pull/430/)
- Support depth-first execution of mapped tasks and tracking of both the static "parent" and dynamic "children" via `Mapped` states - [485](https://github.com/PrefectHQ/prefect/pull/485)

Minor Features

- Add new `TimedOut` state for task execution timeouts - [255](https://github.com/PrefectHQ/prefect/issues/255)
- Use timezone-aware dates throughout Prefect - [325](https://github.com/PrefectHQ/prefect/pull/325)
- Add `description` and `tags` arguments to `Parameters` - [318](https://github.com/PrefectHQ/prefect/pull/318)
- Allow edge `key` checks to be skipped in order to create "dummy" flows from metadata - [319](https://github.com/PrefectHQ/prefect/pull/319)
- Add new `names_only` keyword to `flow.parameters` - [337](https://github.com/PrefectHQ/prefect/pull/337)
- Add utility for building GraphQL queries and simple schemas from Python objects - [342](https://github.com/PrefectHQ/prefect/pull/342)
- Add links to downloadable Jupyter notebooks for all tutorials - [212](https://github.com/PrefectHQ/prefect/issues/212)
- Add `to_dict` convenience method for `DotDict` class - [341](https://github.com/PrefectHQ/prefect/issues/341)
- Refactor requirements to a custom `ini` file specification - [347](https://github.com/PrefectHQ/prefect/pull/347)
- Refactor API documentation specification to `toml` file - [361](https://github.com/PrefectHQ/prefect/pull/361)
- Add new SQLite tasks for basic SQL scripting and querying - [291](https://github.com/PrefectHQ/prefect/issues/291)
- Executors now pass `map_index` into the `TaskRunner`s - [373](https://github.com/PrefectHQ/prefect/pull/373)
- All schedules support `start_date` and `end_date` parameters - [375](https://github.com/PrefectHQ/prefect/pull/375)
- Add `DateTime` marshmallow field for timezone-aware serialization - [378](https://github.com/PrefectHQ/prefect/pull/378)
- Adds ability to put variables into context via the config - [381](https://github.com/PrefectHQ/prefect/issues/381)
- Adds new `client.deploy` method for adding new flows to the Prefect Cloud - [388](https://github.com/PrefectHQ/prefect/issues/388)
- Add `id` attribute to `Task` class - [416](https://github.com/PrefectHQ/prefect/issues/416)
- Add new `Resume` state for resuming from `Paused` tasks - [435](https://github.com/PrefectHQ/prefect/issues/435)
- Add support for heartbeats - [436](https://github.com/PrefectHQ/prefect/issues/436)
- Add new `Submitted` state for signaling that `Scheduled` tasks have been handled - [445](https://github.com/PrefectHQ/prefect/issues/445)
- Add ability to add custom environment variables and copy local files into `ContainerEnvironment`s - [453](https://github.com/PrefectHQ/prefect/issues/453)
- Add `set_secret` method to Client for creating and setting the values of user secrets - [452](https://github.com/PrefectHQ/prefect/issues/452)
- Refactor runners into `CloudTaskRunner` and `CloudFlowRunner` classes - [431](https://github.com/PrefectHQ/prefect/issues/431)
- Added functions for loading default `engine` classes from config - [477](https://github.com/PrefectHQ/prefect/pull/477)

Fixes

- Fixed issue with `GraphQLResult` reprs - [374](https://github.com/PrefectHQ/prefect/pull/374)
- `CronSchedule` produces expected results across daylight savings time transitions - [375](https://github.com/PrefectHQ/prefect/pull/375)
- `utilities.serialization.Nested` properly respects `marshmallow.missing` values - [398](https://github.com/PrefectHQ/prefect/pull/398)
- Fixed issue in capturing unexpected mapping errors during task runs - [409](https://github.com/PrefectHQ/prefect/pull/409)
- Fixed issue in `flow.visualize()` so that mapped flow states can be passed and colored - [387](https://github.com/PrefectHQ/prefect/issues/387)
- Fixed issue where `IntervalSchedule` was serialized at "second" resolution, not lower - [427](https://github.com/PrefectHQ/prefect/pull/427)
- Fixed issue where `SKIP` signals were preventing multiple layers of mapping - [455](https://github.com/PrefectHQ/prefect/issues/455)
- Fixed issue with multi-layer mapping in `flow.visualize()` - [454](https://github.com/PrefectHQ/prefect/issues/454)
- Fixed issue where Prefect Cloud `cached_inputs` weren't being used locally - [434](https://github.com/PrefectHQ/prefect/issues/434)
- Fixed issue where `Config.set_nested` would have an error if the provided key was nested deeper than an existing terminal key - [479](https://github.com/PrefectHQ/prefect/pull/479)
- Fixed issue where `state_handlers` were not called for certain signals - [494](https://github.com/PrefectHQ/prefect/pull/494)

Breaking Changes

- Remove `NoSchedule` and `DateSchedule` schedule classes - [324](https://github.com/PrefectHQ/prefect/pull/324)
- Change `serialize()` method to use schemas rather than custom dict - [318](https://github.com/PrefectHQ/prefect/pull/318)
- Remove `timestamp` property from `State` classes - [305](https://github.com/PrefectHQ/prefect/pull/305)
- Remove the custom JSON encoder library at `prefect.utilities.json` - [336](https://github.com/PrefectHQ/prefect/pull/336)
- `flow.parameters` now returns a set of parameters instead of a dictionary - [337](https://github.com/PrefectHQ/prefect/pull/337)
- Renamed `to_dotdict` -> `as_nested_dict` - [339](https://github.com/PrefectHQ/prefect/pull/339)
- Moved `prefect.utilities.collections.GraphQLResult` to `prefect.utilities.graphql.GraphQLResult` - [371](https://github.com/PrefectHQ/prefect/pull/371)
- `SynchronousExecutor` now does _not_ do depth first execution for mapped tasks - [373](https://github.com/PrefectHQ/prefect/pull/373)
- Renamed `prefect.utilities.serialization.JSONField` -> `JSONCompatible`, removed its `max_size` feature, and no longer automatically serialize payloads as strings - [376](https://github.com/PrefectHQ/prefect/pull/376)
- Renamed `prefect.utilities.serialization.NestedField` -> `Nested` - [376](https://github.com/PrefectHQ/prefect/pull/376)
- Renamed `prefect.utilities.serialization.NestedField.dump_fn` -> `NestedField.value_selection_fn` for clarity - [377](https://github.com/PrefectHQ/prefect/pull/377)
- Local secrets are now pulled from `secrets` in context instead of `_secrets` - [382](https://github.com/PrefectHQ/prefect/pull/382)
- Remove Task and Flow descriptions, Flow project & version attributes - [383](https://github.com/PrefectHQ/prefect/issues/383)
- Changed `Schedule` parameter from `on_or_after` to `after` - [396](https://github.com/PrefectHQ/prefect/issues/396)
- Environments are immutable and return `dict` keys instead of `str`; some arguments for `ContainerEnvironment` are removed - [398](https://github.com/PrefectHQ/prefect/pull/398)
- `environment.run()` and `environment.build()`; removed the `flows` CLI and replaced it with a top-level CLI command, `prefect run` - [400](https://github.com/PrefectHQ/prefect/pull/400)
- The `set_temporary_config` utility now accepts a single dict of multiple config values, instead of just a key/value pair, and is located in `utilities.configuration` - [401](https://github.com/PrefectHQ/prefect/pull/401)
- Bump `click` requirement to 7.0, which changes underscores to hyphens at CLI - [409](https://github.com/PrefectHQ/prefect/pull/409)
- `IntervalSchedule` rejects intervals of less than one minute - [427](https://github.com/PrefectHQ/prefect/pull/427)
- `FlowRunner` returns a `Running` state, not a `Pending` state, when flows do not finish - [433](https://github.com/PrefectHQ/prefect/pull/433)
- Remove the `task_contexts` argument from `FlowRunner.run()` - [440](https://github.com/PrefectHQ/prefect/pull/440)
- Remove the leading underscore from Prefect-set context keys - [446](https://github.com/PrefectHQ/prefect/pull/446)
- Removed throttling tasks within the local cluster - [470](https://github.com/PrefectHQ/prefect/pull/470)
- Even `start_tasks` will not run before their state's `start_time` (if the state is `Scheduled`) - [474](https://github.com/PrefectHQ/prefect/pull/474)
- `DaskExecutor`'s "processes" keyword argument was renamed "local_processes" - [477](https://github.com/PrefectHQ/prefect/pull/477)
- Removed the `mapped` and `map_index` kwargs from `TaskRunner.run()`. These values are now inferred automatically - [485](https://github.com/PrefectHQ/prefect/pull/485)
- The `upstream_states` dictionary used by the Runners only includes `State` values, not lists of `States`. The use case that required lists of `States` is now covered by the `Mapped` state. - [485](https://github.com/PrefectHQ/prefect/pull/485)

Major Features

- Refactor `FlowRunner` and `TaskRunner` into a modular `Runner` pipelines - [260](https://github.com/PrefectHQ/prefect/pull/260), [#267](https://github.com/PrefectHQ/prefect/pull/267)
- Add configurable `state_handlers` for `FlowRunners`, `Flows`, `TaskRunners`, and `Tasks` - [264](https://github.com/PrefectHQ/prefect/pull/264), [#267](https://github.com/PrefectHQ/prefect/pull/267)
- Add gmail and slack notification state handlers w/ tutorial - [274](https://github.com/PrefectHQ/prefect/pull/274), [#294](https://github.com/PrefectHQ/prefect/pull/294)

Minor Features

- Add a new method `flow.get_tasks()` for easily filtering flow tasks by attribute - [242](https://github.com/PrefectHQ/prefect/pull/242)
- Add new `JinjaTemplateTask` for easily rendering jinja templates - [200](https://github.com/PrefectHQ/prefect/issues/200)
- Add new `PAUSE` signal for halting task execution - [246](https://github.com/PrefectHQ/prefect/pull/246)
- Add new `Paused` state corresponding to `PAUSE` signal, and new `pause_task` utility - [251](https://github.com/PrefectHQ/prefect/issues/251)
- Add ability to timeout task execution for all executors except `DaskExecutor(processes=True)` - [240](https://github.com/PrefectHQ/prefect/issues/240)
- Add explicit unit test to check Black formatting (Python 3.6+) - [261](https://github.com/PrefectHQ/prefect/pull/261)
- Add ability to set local secrets in user config file - [231](https://github.com/PrefectHQ/prefect/issues/231), [#274](https://github.com/PrefectHQ/prefect/pull/274)
- Add `is_skipped()` and `is_scheduled()` methods for `State` objects - [266](https://github.com/PrefectHQ/prefect/pull/266), [#278](https://github.com/PrefectHQ/prefect/pull/278)
- Adds `now()` as a default `start_time` for `Scheduled` states - [278](https://github.com/PrefectHQ/prefect/pull/278)
- `Signal` classes now pass arguments to underlying `State` objects - [279](https://github.com/PrefectHQ/prefect/pull/279)
- Run counts are tracked via `Retrying` states - [281](https://github.com/PrefectHQ/prefect/pull/281)

Fixes

- Flow consistently raises if passed a parameter that doesn't exist - [149](https://github.com/PrefectHQ/prefect/issues/149)

Breaking Changes

- Renamed `scheduled_time` -> `start_time` in `Scheduled` state objects - [278](https://github.com/PrefectHQ/prefect/pull/278)
- `TaskRunner.check_for_retry` no longer checks for `Retry` states without `start_time` set - [278](https://github.com/PrefectHQ/prefect/pull/278)
- Swapped the position of `result` and `message` attributes in State initializations, and started storing caught exceptions as results - [283](https://github.com/PrefectHQ/prefect/issues/283)

Major Features

- Local parallelism with `DaskExecutor` - [151](https://github.com/PrefectHQ/prefect/issues/151), [#186](https://github.com/PrefectHQ/prefect/issues/186)
- Resource throttling based on `tags` - [158](https://github.com/PrefectHQ/prefect/issues/158), [#186](https://github.com/PrefectHQ/prefect/issues/186)
- `Task.map` for mapping tasks - [186](https://github.com/PrefectHQ/prefect/issues/186)
- Added `AirFlow` utility for importing Airflow DAGs as Prefect Flows - [232](https://github.com/PrefectHQ/prefect/pull/232)

Minor Features

- Use Netlify to deploy docs - [156](https://github.com/prefecthq/prefect/issues/156)
- Add changelog - [153](https://github.com/prefecthq/prefect/issues/153)
- Add `ShellTask` - [150](https://github.com/prefecthq/prefect/issues/150)
- Base `Task` class can now be run as a dummy task - [191](https://github.com/PrefectHQ/prefect/pull/191)
- New `return_failed` keyword to `flow.run()` for returning failed tasks - [205](https://github.com/PrefectHQ/prefect/pull/205)
- some minor changes to `flow.visualize()` for visualizing mapped tasks and coloring nodes by state - [202](https://github.com/PrefectHQ/prefect/issues/202)
- Added new `flow.replace()` method for swapping out tasks within flows - [230](https://github.com/PrefectHQ/prefect/pull/230)
- Add `debug` kwarg to `DaskExecutor` for optionally silencing dask logs - [209](https://github.com/PrefectHQ/prefect/issues/209)
- Update `BokehRunner` for visualizing mapped tasks - [220](https://github.com/PrefectHQ/prefect/issues/220)
- Env var configuration settings are typed - [204](https://github.com/PrefectHQ/prefect/pull/204)
- Implement `map` functionality for the `LocalExecutor` - [233](https://github.com/PrefectHQ/prefect/issues/233)

Fixes

- Fix issue with Versioneer not picking up git tags - [146](https://github.com/prefecthq/prefect/issues/146)
- `DotDicts` can have non-string keys - [193](https://github.com/prefecthq/prefect/issues/193)
- Fix unexpected behavior in assigning tags using contextmanagers - [190](https://github.com/PrefectHQ/prefect/issues/190)
- Fix bug in initialization of Flows with only `edges` - [225](https://github.com/PrefectHQ/prefect/pull/225)
- Remove "bottleneck" when creating pipelines of mapped tasks - [224](https://github.com/PrefectHQ/prefect/pull/224)

Breaking Changes

- Runner refactor - [221](https://github.com/PrefectHQ/prefect/pull/221)
- Cleaned up signatures of `TaskRunner` methods - [171](https://github.com/prefecthq/prefect/issues/171)
- Locally, Python 3.4 users can not run the more advanced parallel executors (`DaskExecutor`) [186](https://github.com/PrefectHQ/prefect/issues/186)