Add python devShell to nix flake

Adds a top-level python devShell to the nix flake which creates a python
virtual environment with all necessary dependencies installed.

Now, assuming Docker is running and nix is installed on the system, a
developer can simply run `nix develop .#python` and have a shell with
all the requirements to run `python -m unittest --verbose` setup,
or import the `payjoin` package (locally built) to their project.

Author: thebrandonlucas

flake.nix

@@ -93,6 +93,52 @@
             "payjoin-directory" = "";
           };
 
+        # Python-specific configuration
+        pythonVersion = pkgs.python3;
+        pythonEnv = pythonVersion.withPackages (ps: with ps; [
+          virtualenv
+          pip
+        ]);
+
+        # Determine platform for generate script
+        supportedPlatforms = {
+          "x86_64-linux" = "linux";
+          "aarch64-linux" = "linux";
+          "x86_64-darwin" = "macos";
+          "aarch64-darwin" = "macos";
+        };
+        platform = supportedPlatforms.${system} or (throw "Unsupported platform: ${system}. Supported platforms: ${builtins.concatStringsSep ", " (builtins.attrNames supportedPlatforms)}");
+
+        # Python devShell
+        pythonDevShell = pkgs.mkShell {
+          name = "python-dev";
+          buildInputs = with pkgs; [
+            pythonEnv
+            bash
+          ];
+
+          # Environment variables and shell hook
+          shellHook = ''
+            export LD_LIBRARY_PATH=${pkgs.lib.makeLibraryPath [pkgs.openssl]}:$LD_LIBRARY_PATH
+            cd payjoin-ffi/python
+            # Create and activate virtual environment
+            python -m venv venv
+            source venv/bin/activate
+            # Install dependencies, allowing PyPI fetches for version mismatches
+            pip install --requirement requirements.txt --requirement requirements-dev.txt
+            # Generate bindings, setting PYBIN to the venv's python binary
+            export PYBIN=./venv/bin/python
+            bash ./scripts/generate_${platform}.sh
+            # Set CARGO_TOML_PATH for setup.py
+            export CARGO_TOML_PATH=${./.}/Cargo.toml
+            # Build the wheel
+            python setup.py bdist_wheel --verbose
+
+            # Install payjoin
+            pip install ./dist/payjoin-*.whl
+          '';
+        };
+
         devShells = builtins.mapAttrs (_name: craneLib:
           craneLib.devShell {
             packages = with pkgs; [
@@ -115,7 +161,10 @@
             // args);
       in {
         packages = packages;
-        devShells = devShells // {default = devShells.nightly;};
+        devShells = devShells // {
+          default = devShells.nightly;
+          python = pythonDevShell;
+        };
         formatter = pkgs.alejandra;
         checks =
           packages

payjoin-ffi/python/README.md

@@ -1,21 +1,28 @@
 # Payjoin
 
-Welcome to the Python language bindings for the [Payjoin Dev Kit](https://payjoindevkit.org/)! Let's get you up and running with some smooth transactions and a sprinkle of fun.
+Welcome to the Python language bindings for the [Payjoin Dev Kit](https://payjoindevkit.org/)!
 
 ## Install from PyPI
 
-Grab the latest release with a simple:
+To grab the latest release:
 
-```shell
+```sh
 pip install payjoin
 ```
 
-## Running Tests
+## Building the Package
 
-Follow these steps to clone the repository and run the tests.
+If you have [nix](https://nixos.org/download/) installed, you can simply run:
+
+```sh
+nix develop .#python
+```
 
+This will get you up and running with a shell containing the dependencies you need.
 
-```shell
+Otherwise, follow these steps to clone the repository and build the package:
+
+```sh
 git clone https://github.com/payjoin/rust-payjoin.git
 cd rust-payjoin/payjoin-ffi/python
 
@@ -24,40 +31,32 @@ python -m venv venv
 source venv/bin/activate
 
 # Install dependencies
+# NOTE: requirements-dev.txt only needed when running tests
 pip install --requirement requirements.txt --requirement requirements-dev.txt
 
-# Generate the bindings (use the script appropriate for your platform)
+# Generate the bindings (use the script appropriate for your platform (linux or macos))
 PYBIN="./venv/bin/" bash ./scripts/generate_<platform>.sh
 
 # Build the wheel
 python setup.py bdist_wheel --verbose
 
 # Force reinstall payjoin
 pip install ./dist/payjoin-<version>.whl --force-reinstall
+```
+
+If all goes well, you should be able to run the Python interpreter and import `payjoin`:
 
+```sh
+python
+import payjoin
+```
+
+## Running Tests
+
+```sh
 # Run all tests
 python -m unittest --verbose
 ```
 
 Note that you'll need Docker to run the integration tests. If you get a "Failed to start container" error, ensure the Docker engine is running on your machine.
 You can [filter which tests](https://docs.python.org/3/library/unittest.html#command-line-interface) to run by passing a file or test name as argument.
-
-## Building the Package
-
-```shell
-# Setup a python virtual environment
-python -m venv venv
-source venv/bin/activate
-
-# Install dependencies
-pip install --requirement requirements.txt
-
-# Generate the bindings (use the script appropriate for your platform)
-PYBIN="./venv/bin/" bash ./scripts/generate_<platform>.sh
-
-# Build the wheel
-python setup.py --verbose bdist_wheel
-
-```
-We hope everything worked smoothly! Now go forth test, and may your test results be as reliable as the Bitcoin blockchain itself!
-₿🔒🤝