Merge pull request #3753 from Cologler/patch-2

Update core.py

Author: Frost Ming

news/3753.trivial.rst

@@ -0,0 +1 @@
+Improve the error message of ``pipenv --py`` when virtualenv can't be found.

pipenv/core.py

@@ -1775,6 +1775,17 @@ def ensure_lockfile(keep_outdated=False, pypi_mirror=None):
 
 
 def do_py(system=False):
+    if not project.virtualenv_exists:
+        click.echo(
+            "{}({}){}".format(
+                crayons.red("No virtualenv has been created for this project "),
+                crayons.white(project.project_directory, bold=True),
+                crayons.red(" yet!")
+            ),
+            err=True,
+        )
+        return    
+    
     try:
         click.echo(which("python", allow_global=system))
     except AttributeError: