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If you are already a Python 3 user, you should not encounter a lot of

disruption. Please check that the libraries you use follow best practices not

to break for Python 3 users.

disruption. Please still check that the libraries you use follow best practices

not to break for Python 2 users. Python is a community regardless of which

python version you have to a decide to run, making sure that things works make

the community strong.

Make sure you have Pip >= 9.0, this is especially important if you have Python

2 installations. Having pip 9.0+ will not insure that you install will not

break, but they are more likely not to. Having a version off pip <9.0 can lead

your system to try to upgrade to non-compatible versions of Python packages

even if these are marked as non-compatible.

Make as many other_users_ as possible to install pip >=9.0, for the

transition, it is the slowest part of the ecosystem to update, and is the only

piece that concern all all installations.

If you are on a system that will not install python wheel and use`setuptools`,

make sure you have setuptools >=24.2.0, or building Python 3 only libraries

might fail, even on Python 2.

If you are using a custom local package index, for example if you are working

at a company, make sure it implement correctly pep-512 and let pip knows about

the`python_requires` field.

at a company with private packages, make sure it implement correctly pep-503

and let pip knows aboutthe`python_requires` field.

Note that at the time of this writing the patches to`pypi.python.org` are not

deployed yet but should hopefully be deployed soon.

Things to speak about:

- Be on recent enough setuptools, since[This

PR](https://github.com/pypa/setuptools/pull/631), 24.2.0 (or above, July 20,

2016, Xavier Fernandez PR.)

Add the followign to your setup.py

As a library author one of the most important factor in a smooth transition is

planning and communication, letting your user base know in advance that the

transition is happening and what step to take is critical for a transition.

For your library code here the steps you need to take to ensure that

installation will fail in the least number of case:

You need to release your new packages version with[setuptools] version 24.2.0

or above, or use one of the alternate package manager that can set the

[`python_require`] metadata field. Without this, pip 9.0**will try** to

install non-compatible version of your software on Python 2. This version of

setuptools is recent (July 20, 2016) and this possible thank to the[work of

Xavier Fernandez](https://github.com/pypa/setuptools/pull/631)

Add the following to your`setup.py`

change >=

Changes`>=3.3` accordingly depending on what version your library decides to

support.

This will make[PyPI aware](linkto mike's PR on warehouse) that your package is

Python 3 only, and[allow pip](link to pip's PR) to be[made aware of this](link to PyPI PR).

- Add a warning at_runtime_ early on master (before switching to Python 3