Define a fake Python binary in fake Conda env

conda_lock/conda_solver.py

@@ -580,4 +580,41 @@ def fake_conda_environment(
 
             with open(conda_meta / (truncated_path.name + ".json"), "w") as f:
                 json.dump(entry, f, indent=2)
+            make_fake_python_binary(prefix)
         yield prefix
+
+
+FAKE_PYTHON_BINARY = """\
+#!/usr/bin/env python
+
+import sys
+import shlex
+
+cmd = shlex.join(sys.argv)
+
+stderr_message = f'''\
+This is a fake python binary generated by conda-lock.
+
+It prevents libmamba from failing when it tries to check for installed pip packages.
+
+This was called as:
+    {cmd}
+'''
+
+print(stderr_message, file=sys.stderr, flush=True, end='')
+
+if "-m pip" not in cmd:
+    raise RuntimeError("Expected to invoke pip module with `-m pip`.")
+"""
+
+
+def make_fake_python_binary(prefix: str) -> None:
+    """Create a fake python binary in the given prefix.
+
+    This is intended to prevent failure of `PrefixData.load_site_packages`
+    which was introduced in libmamba v2.
+    """
+    fake_python_binary = pathlib.Path(prefix) / "bin" / "python"
+    fake_python_binary.parent.mkdir(parents=True, exist_ok=True)
+    fake_python_binary.write_text(FAKE_PYTHON_BINARY)
+    fake_python_binary.chmod(0o755)