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@ -78,18 +78,16 @@ containing
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```nix
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with import <nixpkgs> {};
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(pkgs.python35.buildEnv.override {
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extraLibs = with pkgs.python35Packages; [ numpy toolz ];
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}).env
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(pkgs.python35.withPackages (ps: [ps.numpy ps.toolz])).env
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```
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executing `nix-shell` gives you again a Nix shell from which you can run Python.
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What's happening here?
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1. We begin with importing the Nix Packages collections. `import <nixpkgs>` import the `<nixpkgs>` function, `{}` calls it and the `with` statement brings all attributes of `nixpkgs` in the local scope. Therefore we can now use `pkgs`.
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2. Then we create a Python 3.5 environment with `pkgs.buildEnv`. Because we want to use it with a custom set of Python packages, we override it.
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3. The `extraLibs` argument of the original `buildEnv` function can be used to specify which packages should be included. We want `numpy` and `toolz`. Again, we use the `with` statement to bring a set of attributes into the local scope.
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4. And finally, for in interactive use we return the environment.
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2. Then we create a Python 3.5 environment with the `withPackages` function.
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3. The `withPackages` function expects us to provide a function as an argument that takes the set of all python packages and returns a list of packages to include in the environment. Here, we select the packages `numpy` and `toolz` from the package set.
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4. And finally, for in interactive use we return the environment by using the `env` attribute.
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### Developing with Python
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@ -187,10 +185,7 @@ with import <nixpkgs> {};
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};
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};
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in pkgs.python35.buildEnv.override rec {
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extraLibs = [ pkgs.python35Packages.numpy toolz ];
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}
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in pkgs.python35.withPackages (ps: [ps.numpy toolz])
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).env
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```
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@ -199,8 +194,11 @@ locally defined package as well as `numpy` which is build according to the
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definition in Nixpkgs. What did we do here? Well, we took the Nix expression
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that we used earlier to build a Python environment, and said that we wanted to
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include our own version of `toolz`. To introduce our own package in the scope of
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`buildEnv.override` we used a
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`withPackages` we used a
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[`let`](http://nixos.org/nix/manual/#sec-constructs) expression.
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You can see that we used `ps.numpy` to select numpy from the nixpkgs package set (`ps`).
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But we do not take `toolz` from the nixpkgs package set this time.
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Instead, `toolz` will resolve to our local definition that we introduced with `let`.
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### Handling dependencies
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@ -359,7 +357,7 @@ own packages. The important functions here are `import` and `callPackage`.
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### Including a derivation using `callPackage`
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Earlier we created a Python environment using `buildEnv`, and included the
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Earlier we created a Python environment using `withPackages`, and included the
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`toolz` package via a `let` expression.
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Let's split the package definition from the environment definition.
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@ -394,9 +392,7 @@ with import <nixpkgs> {};
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( let
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toolz = pkgs.callPackage ~/path/to/toolz/release.nix { pkgs=pkgs; buildPythonPackage=pkgs.python35Packages.buildPythonPackage; };
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in pkgs.python35.buildEnv.override rec {
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extraLibs = [ pkgs.python35Packages.numpy toolz ];
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}
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in pkgs.python35.withPackages (ps: [ ps.numpy toolz ])
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).env
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```
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@ -450,6 +446,7 @@ Each interpreter has the following attributes:
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- `libPrefix`. Name of the folder in `${python}/lib/` for corresponding interpreter.
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- `interpreter`. Alias for `${python}/bin/${executable}`.
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- `buildEnv`. Function to build python interpreter environments with extra packages bundled together. See section *python.buildEnv function* for usage and documentation.
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- `withPackages`. Simpler interface to `buildEnv`. See section *python.withPackages function* for usage and documentation.
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- `sitePackages`. Alias for `lib/${libPrefix}/site-packages`.
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- `executable`. Name of the interpreter executable, ie `python3.4`.
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@ -548,7 +545,7 @@ Python environments can be created using the low-level `pkgs.buildEnv` function.
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This example shows how to create an environment that has the Pyramid Web Framework.
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Saving the following as `default.nix`
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with import {};
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with import <nixpkgs> {};
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python.buildEnv.override {
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extraLibs = [ pkgs.pythonPackages.pyramid ];
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@ -565,7 +562,7 @@ You can also use the `env` attribute to create local environments with needed
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packages installed. This is somewhat comparable to `virtualenv`. For example,
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running `nix-shell` with the following `shell.nix`
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with import {};
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with import <nixpkgs> {};
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(python3.buildEnv.override {
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extraLibs = with python3Packages; [ numpy requests ];
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@ -581,6 +578,37 @@ specified packages in its path.
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* `postBuild`: Shell command executed after the build of environment.
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* `ignoreCollisions`: Ignore file collisions inside the environment (default is `false`).
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#### python.withPackages function
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The `python.withPackages` function provides a simpler interface to the `python.buildEnv` functionality.
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It takes a function as an argument that is passed the set of python packages and returns the list
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of the packages to be included in the environment. Using the `withPackages` function, the previous
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example for the Pyramid Web Framework environment can be written like this:
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with import <nixpkgs> {};
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python.withPackages (ps: [ps.pyramid])
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`withPackages` passes the correct package set for the specific interpreter version as an
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argument to the function. In the above example, `ps` equals `pythonPackages`.
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But you can also easily switch to using python3:
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with import <nixpkgs> {};
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python3.withPackages (ps: [ps.pyramid])
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Now, `ps` is set to `python3Packages`, matching the version of the interpreter.
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As `python.withPackages` simply uses `python.buildEnv` under the hood, it also supports the `env`
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attribute. The `shell.nix` file from the previous section can thus be also written like this:
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with import <nixpkgs> {};
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(python33.withPackages (ps: [ps.numpy ps.requests])).env
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In contrast to `python.buildEnv`, `python.withPackages` does not support the more advanced options
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such as `ignoreCollisions = true` or `postBuild`. If you need them, you have to use `python.buildEnv`.
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### Development mode
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Development or editable mode is supported. To develop Python packages
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@ -591,7 +619,7 @@ Warning: `shellPhase` is executed only if `setup.py` exists.
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Given a `default.nix`:
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with import {};
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with import <nixpkgs> {};
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buildPythonPackage { name = "myproject";
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@ -649,9 +677,8 @@ newpkgs = pkgs.overridePackages(self: super: rec {
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self = python35Packages // { pandas = python35Packages.pandas.override{name="foo";};};
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};
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});
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in newpkgs.python35.buildEnv.override{
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extraLibs = [newpkgs.python35Packages.blaze ];
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}).env
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in newpkgs.python35.withPackages (ps: [ps.blaze])
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).env
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```
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A typical use case is to switch to another version of a certain package. For example, in the Nixpkgs repository we have multiple versions of `django` and `scipy`.
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In the following example we use a different version of `scipy`. All packages in `newpkgs` will now use the updated `scipy` version.
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@ -665,9 +692,8 @@ newpkgs = pkgs.overridePackages(self: super: rec {
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self = python35Packages // { scipy = python35Packages.scipy_0_16;};
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};
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});
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in pkgs.python35.buildEnv.override{
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extraLibs = [newpkgs.python35Packages.blaze ];
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}).env
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in newpkgs.python35.withPackages (ps: [ps.blaze])
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).env
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```
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The requested package `blaze` depends upon `pandas` which itself depends on `scipy`.
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Frederik Rietdijk