Ddtrace

**Distributed Tracing**
Add distributed tracing using integration settings for the following libraries/frameworks:
* `bottle` (382)
* `requests` (372)
* `pyramid` (403)

**Improvements**
* [core] provide constants to pick Priority Sampling values (391)
* [django] add support for Django Rest Framework (389)
* [tooling] add missing classifiers for pypi (395 -- thanks PCManticore)
* [tornado] patch `concurrent.futures` if available, improving the way traces are built when propagation happens between threads (362 -- thanks codywilbourn)

**Bugfixes**
* [httplib] don't overwrite return value (380 -- thanks yoichi)
* [psycopg2] patch all imports of `register_type` (393 -- thanks stj)
* [pyramid] keep request as part of `render` kwargs (384 -- thanks joual)
* [pyramid] use pyramid `HTTPExceptions` as valid response types (401, 386 -- thanks TylerLubeck)
* [requests] add `unpatch` and double-patch protection (404)
* [flask] don't override code of already handled errors (390, 409)
* [flask] allow mutability of `resource` field within request (353, 410)

Read the [full changeset](https://github.com/DataDog/dd-trace-py/compare/v0.10.0...v0.10.1).
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**Distributed Sampling (beta)**

New feature that propagates the sampling priority across services. This is useful to mark traces as "don’t keep the trace" or "must have" when distributed tracing is used. This new functionality requires at least the Datadog Agent 5.19+. Frameworks with out-of-the-box support are: Django, Flask, Tornado (358, 325, 359, 364, 366, 365, 371, [docs](http://pypi.datadoghq.com/trace/docs/#priority-sampling))

**Improvements**
* [core] update the Context propagation API, that includes a new way to retrieve and set the current active `Span` context. (339)
* [core] implement Propagators API to simplify Distributed Tracing. You can use `HTTPPropagator` class to inject and extract the tracing context in HTTP headers (363, 374 [docs](http://pypi.datadoghq.com/trace/docs/#ddtrace.propagation.http.HTTPPropagator))
* [celery] use service name from `DATADOG_SERVICE_NAME` env var, if defined (347 -- thanks miketheman)
* [django] respect env Agent host and port if defined (354 -- thanks spesnova)

**Bugfixes**
* [pylons] handle exception with non standard 'code' attribute (350)
* [pyramid] the application was not traced when the tween list was explicitly specified (349)

Read the full [changeset](https://github.com/DataDog/dd-trace-py/compare/v0.9.2...v0.10.0)
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**New features**
* [django] disable database or cache instrumentation via settings so that each Django component instrumentation can be disabled (314, [docs](http://localhost:8000/#module-ddtrace.contrib.django) -- thanks mcanaves)
* [django] it's not required anymore to add the Django middleware because the Django app ensures that it is installed. You can safely remove `ddtrace.contrib.django.TraceMiddleware` for your middleware list after the upgrade. This is not mandatory but suggested (314, 346)
* [cassandra] trace `execute_async()` operations (333)

**Bugfixes**
* [mysql] prevent the Pin from attaching empty tags (327)
* [django] fixed the initialization order to prevent logs when the tracer is disabled (334)
* [sqlite3] add tests to ensure that services are properly sent (337)
* [pyramid] fixed Pyramid crash when 'include()' is used with relative import paths (342)
* [pylons] re-raise the exception with the original traceback in case of errors. Before Pylons exceptions were correctly handled but hidden by the tracing middleware. (317)
* [pyramid] disable autocommit in Pyramid patching, to avoid altering the `Configurator` behavior (343)
* [flask] fix Flask instrumentation that didn't close Jinja spans if an error was thrown (344)

**Integration coverage**
* officially support ElasticSearch 1.6+ (341)

**Documentation**
* fixed usage examples for `patch_all()` and `patch()` (321 -- thanks gomlgs)
* added a section about updating the hostname and port (335)

Read the [full changeset](https://github.com/DataDog/dd-trace-py/compare/v0.9.1...v0.9.2).
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**New features**
* [core] add a processing pipeline to the `AsyncWorker`, so that traces can be filtered easily. This change doesn't have any performance impact with existing installations, and is expected to work well with async frameworks / libraries (303, [docs](http://pypi.datadoghq.com/trace/docs/#trace-filtering))
* [core] add language and library version metadata to keep track of them in the Datadog Agent. All values are sent via headers (289)

**Bugfixes**
* [aiobotocore] update `async with` context manager so that it returns the wrapper instead of the wrapped object (307)
* [boto, botocore] change the service metadata app for AWS with a more meaningful name (315)

**Documentation**
* improving documentation so that it's more explicit how a framework should be auto-instrumented (305, 308)
* add the list of auto-instrumented modules (306)

Read the [full changeset](https://github.com/DataDog/dd-trace-py/compare/v0.9.0...v0.9.1).
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**New features**

* [core] add process ID in root spans metadata (293)

**Improvements**

* [falcon] extended support for Falcon 1.2; improved error handling (295)
* [gevent] create a new `Context` when a Greenlet is created so that the tracing context is automatically propagated with the right parenting (287)
* [asyncio] providing helpers and `patch()` method to automatically propagate the tracing context between different asyncio tasks (260 297, [docs](http://pypi.datadoghq.com/trace/docs/#module-ddtrace.contrib.asyncio) -- thanks thehesiod)
* [aiohttp] add experimental feature to continue a trace from request headers (259, [docs](http://pypi.datadoghq.com/trace/docs/#module-ddtrace.contrib.aiohttp) -- thanks thehesiod)
* [django] add `DEFAULT_DATABASE_PREFIX` setting to append a prefix to database service (291, [docs](http://pypi.datadoghq.com/trace/docs/#module-ddtrace.contrib.django) -- thanks jairhenrique)

**Bugfixes**

* [logging] use specific logger instead of the root one in `monkey.py` module (281)
* [django] `ddtrace` exception middleware catches exceptions even if a custom middleware returns a `Response` object (278)
* [pylons] handle correctly the http status code when it's wrongly formatted (284)
* [django] request resource handles the case where the `View` is a partial function (292)
* [flask] attach stack trace to Flask errors (302)

**New integrations**

* [httplib] add patching for `httplib` and `http.lib`(137 -- thanks brettlangdon)
* [aio-libs] add `aiobotocore` support (257, 298, [docs](http://pypi.datadoghq.com/trace/docs/#module-ddtrace.contrib.aiobotocore) -- thanks thehesiod)
* [aio-libs] add `aiopg` support (258, [docs](http://pypi.datadoghq.com/trace/docs/#module-ddtrace.contrib.aiopg) -- thanks thehesiod)

Read the [full changeset](https://github.com/DataDog/dd-trace-py/compare/v0.8.5...v0.9.0).
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**Bugfixes**

* [flask] add the http method to flask spans (274)
* [sqlite3] changed the app_type to `db` (276)
* [core] `span.set_traceback()`now sets the traceback even if there's no exception (277)

Read the [full changeset][1].

[1]: https://github.com/DataDog/dd-trace-py/compare/v0.8.4...v0.8.5
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