Ddtrace

**Bugfixes**

* [flask] avoid using weak references when Flask is instrumented via Blinker. This resolves initialization issues when the `traced_app = TraceMiddleware(app, ...)` reference goes out of the scope or is garbage collected (273)
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**Improvements**

* [transport] add presampler header (`X-Datadog-Trace-Count`) so that the receiving agent has more information when dealing with sampling (254)
* [docs] updated our documentation (264, 271)

**Bugfixes**
* [core] patch loader raises `PatchException` that is handled in the `patch_all()` when the patch failed. This distinguishes: errors during patch, when an integration is not available and simply when the module is not installed (262)
* [mysql] distinguish `MySQL-Python` instrumentation so that only `mysql-connector` package is patched; this provides better feedback about what library is supported (263, 266)
* [sqlalchemy] provide a `patch()` method that uses the PIN object; this is not a breaking change, but the preferred way to instrument SQLAlchemy is through `patch_all(sqlalchemy=True)` or `patch(sqlalchemy=True)` (261)
* [pylons] catch `BaseException` since a `SystemExit` might've been raised; `500` errors are handled if a timeout occurs (267, 270)
* [pyramid] catch `BaseException` since a `SystemExit` might've been raised; `500` errors are handled if a timeout occurs (269)

Read the [full changeset][1]

[1]: https://github.com/DataDog/dd-trace-py/compare/v0.8.2...v0.8.3
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**Bugfixes**

* [django] handle tuple `INSTALLED_APPS` for Django < 1.9 (253)

Read the [full changeset][1]

[1]: https://github.com/DataDog/dd-trace-py/compare/v0.8.1...v0.8.2
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**Bugfixes**

* [core] fixed `msgpack-python` kwarg usage for versions earlier than `0.4.x` (245)
* [pyramid] add request method to Pyramid trace span resource name (249, thanks johnpkennedy)

Read the [full changeset][1].

[1]: https://github.com/DataDog/dd-trace-py/compare/v0.8.0...v0.8.1
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* [elasticsearch] the PIN object was previously attached to the `elasticsearch` module while now it uses `elasticsearch.Transport`. If you were using the `Pin` to override some tracing settings, you must update your code from:
python
Pin.override(client, service='elasticsearch-traces')

to:
python
Pin.override(client.transport, service='elasticsearch-traces')


**Internals update**
* the Python traces logs and returns error when there is a communication issue with the APM Agent (173)
* the `wrap()` tracer decorator can be extended by Python integrations when the usual approach is not suitable for the given execution context (221)

Read the [full changeset][2].

[1]: http://pypi.datadoghq.com/trace/docs/#module-ddtrace.contrib.tornado
[2]: https://github.com/DataDog/dd-trace-py/compare/v0.7.0...v0.8.0
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**New integrations**
* Add support for `boto` (>=2.29.0) and `botocore` (>= 1.4.51) 209 . Currently these integrations are ignored by autopatching, but can be enabled via `patch_all(boto=True, botocore=True)`

**New features**
* Add the `ddtrace-run` command-line entrypoint to provide tracing without explicit additions to code. More information here http://pypi.datadoghq.com/trace/docs/#get-started 169

**Bugfixes**
* [dbapi] Ensure cursors play well with context managers 231
* [django] Provide a unique `datadog_django` app label to avoid clashes with existing app configs 235
* [pyramid] Ensure pyramid spans have method and route metadata consistent with other web frameworks 220 (thanks johnpkennedy)
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