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python docs: improve override example

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1. Use the same approach like in the overlay example:
   Override `python` instead of `pythonPackages` so that
   `python.pkgs` refers to the new package set like `pythonPackages`.

   This also fixes a bug in the original example where
   `pkgs.fetchgit` was not in scope.

   Add an extra example to illustrate how to override just a
   package set.

2. Fix mix-up between `super` and `self` in the explanation text.
   Also, simplify the explanation.
This commit is contained in:
Erik Arvstedt 2018-07-25 21:29:25 +02:00
parent a8f54972f4
commit 42e3727aa2
1 changed files with 21 additions and 9 deletions
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30
doc/languages-frameworks/python.section.md
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@ -1006,14 +1006,14 @@ folder and not downloaded again.
If you need to change a package's attribute(s) from `configuration.nix` you could do:
```nix
nixpkgs.config.packageOverrides = superP: {
pythonPackages = superP.pythonPackages.override {
overrides = self: super: {
bepasty-server = super.bepasty-server.overrideAttrs ( oldAttrs: {
src = pkgs.fetchgit {
nixpkgs.config.packageOverrides = super: {
python = super.python.override {
packageOverrides = python-self: python-super: {
bepasty-server = python-super.bepasty-server.overrideAttrs (oldAttrs: {
src = super.fetchgit {
url = "https://github.com/bepasty/bepasty-server";
sha256 = "9ziqshmsf0rjvdhhca55sm0x8jz76fsf2q4rwh4m6lpcf8wr0nps";
rev = "e2516e8cf4f2afb5185337073607eb9e84a61d2d";
sha256 = "9ziqshmsf0rjvdhhca55sm0x8jz76fsf2q4rwh4m6lpcf8wr0nps";
};
});
};
@ -1021,11 +1021,23 @@ If you need to change a package's attribute(s) from `configuration.nix` you coul
};
```
If you are using the `bepasty-server` package somewhere, for example in `systemPackages` or indirectly from `services.bepasty`, then a `nixos-rebuild switch` will rebuild the system but with the `bepasty-server` package using a different `src` attribute. This way one can modify `python` based software/libraries easily. Using `self` and `super` one can also alter dependencies (`buildInputs`) between the old state (`self`) and new state (`super`).
If you are using the `bepasty-server` package somewhere, for example in `systemPackages` or indirectly from `services.bepasty`, then a `nixos-rebuild switch` will rebuild the system but with the `bepasty-server` package using a different `src` attribute. This way one can modify `python` based software/libraries easily.
Note that `python-super` refers to the old package set and `python-self`
to the new, overridden version.
To modify only a Python package set instead of a whole Python derivation, use this snippet:
```nix
myPythonPackages = pythonPackages.override {
overrides = self: super: {
bepasty-server = ...;
};
}
```
### How to override a Python package using overlays?
To alter a python package using overlays, you would use the following approach:
Use the following overlay template:
```nix
self: super:
@ -1035,8 +1047,8 @@ self: super:
bepasty-server = python-super.bepasty-server.overrideAttrs (oldAttrs: {
src = self.pkgs.fetchgit {
url = "https://github.com/bepasty/bepasty-server";
sha256 = "9ziqshmsf0rjvdhhca55sm0x8jz76fsf2q4rwh4m6lpcf8wr0nps";
rev = "e2516e8cf4f2afb5185337073607eb9e84a61d2d";
sha256 = "9ziqshmsf0rjvdhhca55sm0x8jz76fsf2q4rwh4m6lpcf8wr0nps";
};
});
};