update Nix file

default.nix

@@ -1,20 +0,0 @@
-with import <nixpkgs> {};
-
-stdenv.mkDerivation {
-  name = "myPythonEnv";
-  buildInputs = with pkgs; [
-    python37Full
-    python37Packages.virtualenv
-  ];
-  src = null;
-  shellHook = ''
-    if [ ! -d .venv ]; then
-      python -m venv .venv
-    fi
-    source .venv/bin/activate
-    pip install --upgrade pip
-    if [ -s requirements.txt ]; then
-      pip install -r requirements.txt
-    fi
-  '';
-}

shell.nix

@@ -0,0 +1,37 @@
+{ pkgs ? import <nixpkgs> {} }:
+pkgs.mkShell {
+  name = "python-environment";
+  buildInputs = with pkgs; [
+    python3
+    python3Packages.virtualenv
+  ];
+  shellHook = ''
+    function log_header {
+      echo -ne "==> \e[32m\e[1m$1\e[0m\n\n"
+    }
+    function log_subheader {
+      echo -ne "--> \e[33m\e[1m$1\e[0m\n\n"
+    }
+    function log {
+      echo -ne "    $1\n"
+    }
+
+    echo ""
+    log_header "python_environment"
+    if [ ! -d .venv ]; then
+      python -m venv .venv
+    fi
+    source .venv/bin/activate
+    log_subheader "upgrading pip"
+    pip install --upgrade pip
+    echo ""
+    if [ -s requirements.txt ]; then
+      log_subheader "found requirements.txt, installing packages"
+      pip install -r requirements.txt
+      echo ""
+    fi
+    log_header "package versions"
+    log "$(python --version)"
+    log "$(pip --version)"
+  '';
+}