From 5bd5293b4e368f307b0b8af5150d0cf77e4d5878 Mon Sep 17 00:00:00 2001
From: Jesse Cirimelli-Low <jcirimel@ucsc.edu>
Date: Mon, 4 May 2026 16:39:33 -0700
Subject: [PATCH] use python venv with nix

---
 .gitignore |  1 +
 Makefile   |  2 +-
 flake.nix  | 15 ++++++++++++++-
 3 files changed, 16 insertions(+), 2 deletions(-)

diff --git a/.gitignore b/.gitignore
index 7b0c7889..dc55dac3 100644
--- a/.gitignore
+++ b/.gitignore
@@ -19,6 +19,7 @@ compiler/tests/results/
 open_pdks/
 dist/
 openram.egg-info/
+.venv/
 sky130A
 sky130B
 gf180mcuA
diff --git a/Makefile b/Makefile
index f2c65a15..f20dbdc6 100644
--- a/Makefile
+++ b/Makefile
@@ -246,5 +246,5 @@ build_library:
 
 # Build and install the openram library
 library: build_library
-	@python3 -m pip install --force dist/openram*.whl
+	@python3 -m pip install --force-reinstall dist/openram*.whl
 .PHONY: library
diff --git a/flake.nix b/flake.nix
index fa72149d..8c6fcee2 100644
--- a/flake.nix
+++ b/flake.nix
@@ -38,11 +38,24 @@
               pkgs.git
               pkgs.gnumake
               pkgs.curl
+
+              # Python + pip (user installs, venvs; prefer Nix where possible)
+              pkgs.python3
+              pkgs.python3Packages.pip
             ];
 
             shellHook = ''
               export OPENRAM_USE_CONDA=0
-              echo "OpenRAM: using tools from Nix devShell"
+              # PEP 668: Nix `python3` is externally managed. Put a repo-local venv first on PATH
+              # so `make library` uses it. Use $PWD (writable checkout), not `toString self` (nix store).
+              OPENRAM_VENV="''${OPENRAM_HOME}/.venv"
+              if [ ! -x "$OPENRAM_VENV/bin/python3" ]; then
+                echo "OpenRAM: creating venv at $OPENRAM_VENV"
+                ${pkgs.python3}/bin/python3 -m venv "$OPENRAM_VENV"
+              fi
+              export VIRTUAL_ENV="$OPENRAM_VENV"
+              export PATH="$OPENRAM_VENV/bin:$PATH"
+              echo "OpenRAM: Nix devShell (venv on PATH: $OPENRAM_VENV)"
             '';
           };
         });