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Doc: how to install a Python environment

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See https://github.com/NixOS/nixpkgs/issues/10597.
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Frederik Rietdijk 2016-07-01 14:29:41 +02:00
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doc/languages-frameworks/python.md
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@ -649,6 +649,56 @@ community to help save time. No tool is preferred at the moment.
## FAQ
### How can I install a working Python environment?
As explained in the user's guide installing individual Python packages
imperatively with `nix-env -i` or declaratively in `environment.systemPackages`
is not supported. However, it is possible to install a Python environment with packages (`python.buildEnv`).
In the following examples we create an environment with Python 3.5, `numpy` and `ipython`.
As you might imagine there is one limitation here, and that's you can install
only one environment at a time. You will notice the complaints about collisions
when you try to install a second environment.
#### Environment defined in separate `.nix` file
Create a file, e.g. `build.nix`, with the following expression
```nix
with import <nixpkgs> {};
with python35Packages;
python.withPackages (ps: with ps; [ numpy ipython ])
```
and install it in your profile with
```
nix-env -if build.nix
```
Now you can use the Python interpreter, as well as the extra packages that you added to the environment.
#### Environment defined in `~/.nixpkgs/config.nix`
If you prefer to, you could also add the environment as a package override to the Nixpkgs set.
```
packageOverrides = pkgs: with pkgs; with python35Packages; {
myEnv = python.withPackages (ps: with ps; [ numpy ipython ]);
};
```
and install it in your profile with
```
nix-env -iA nixos.blogEnv
```
Note that I'm using the attribute path here.
#### Environment defined in `/etc/nixos/configuration.nix`
For the sake of completeness, here's another example how to install the environment system-wide.
```nix
environment.systemPackages = with pkgs; [
(python35Packages.python.withPackages (ps: callPackage ../packages/common-python-packages.nix { pythonPackages = ps; }))
];
```
### How to solve circular dependencies?
Consider the packages `A` and `B` that depend on each other. When packaging `B`,