Correctly populate the system python path

news/4315.bugfix.rst

@@ -0,0 +1 @@
+Fix a bug that incorrect Python path will be used when ``--system`` flag is on.

pipenv/core.py

@@ -1946,6 +1946,8 @@ def do_install(
     # Automatically use an activated virtualenv.
     if PIPENV_USE_SYSTEM:
         system = True
+    if system:
+        os.environ["PIPENV_USE_SYSTEM"] = "1"
     # Check if the file is remote or not
     if remote:
         click.echo(

pipenv/environment.py

@@ -267,7 +267,10 @@ class Environment(object):
     def python(self):
         # type: () -> str
         """Path to the environment python"""
-        py = vistir.compat.Path(self.script_basedir).joinpath("python").absolute().as_posix()
+        if os.name == "nt" and not self.is_venv:
+            py = vistir.compat.Path(self.prefix).joinpath("python").absolute().as_posix()
+        else:
+            py = vistir.compat.Path(self.script_basedir).joinpath("python").absolute().as_posix()
         if not py:
             return vistir.compat.Path(sys.executable).as_posix()
         return py