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python/README.md

@@ -68,6 +68,10 @@ This is the defacto image. If you are unsure about what your needs are, you prob
 
 This image makes building derivative images easier. For most use cases, creating a `Dockerfile` in the base of your project directory with the line `FROM python:onbuild` will be enough to create a stand-alone image for your project.
 
+While the `onbuild` variant is really useful for "getting off the ground running" (zero to Dockerized in a short period of time), it's not recommended for long-term usage within a project due to the lack of control over *when* the `ONBUILD` triggers fire (see also [`docker/docker#5714`](https://github.com/docker/docker/issues/5714), [`docker/docker#8240`](https://github.com/docker/docker/issues/8240), [`docker/docker#11917`](https://github.com/docker/docker/issues/11917)).
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+Once you've got a handle on how your project functions within Docker, you'll probably want to adjust your `Dockerfile` to inherit from a non-`onbuild` variant and copy the commands from the `onbuild` variant `Dockerfile` (moving the `ONBUILD` lines to the end and removing the `ONBUILD` keywords) into your own file so that you have tighter control over them and more transparency for yourself and others looking at your `Dockerfile` as to what it does. This also makes it easier to add additional requirements as time goes on (such as installing more packages before performing the previously-`ONBUILD` steps).
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 ## `python:slim`
 
 This image does not contain the common packages contained in the default tag and only contains the minimal packages needed to run `python`. Unless you are working in an environment where *only* the python image will be deployed and you have space constraints, we highly recommend using the default image of this repository.