Fixed #27721 -- Added interface name to shell's IPython/bython import error.

django/core/management/commands/shell.py

@@ -3,7 +3,7 @@ import select
 import sys
 import warnings
 
-from django.core.management.base import BaseCommand
+from django.core.management import BaseCommand, CommandError
 from django.utils.datastructures import OrderedSet
 from django.utils.deprecation import RemovedInDjango20Warning
 
@@ -108,4 +108,4 @@ class Command(BaseCommand):
                 return getattr(self, shell)(options)
             except ImportError:
                 pass
-        raise ImportError("Couldn't load any of the specified interfaces.")
+        raise CommandError("Couldn't import {} interface.".format(shell))

tests/shell/tests.py

@@ -2,7 +2,7 @@ import sys
 import unittest
 
 from django import __version__
-from django.core.management import call_command
+from django.core.management import CommandError, call_command
 from django.test import SimpleTestCase, mock
 from django.test.utils import captured_stdin, captured_stdout, patch_logger
 
@@ -29,3 +29,24 @@ class ShellCommandTestCase(SimpleTestCase):
             stdin.seek(0)
             call_command('shell')
         self.assertEqual(stdout.getvalue().strip(), '100')
+
+    @mock.patch('django.core.management.commands.shell.select.select')  # [1]
+    @mock.patch.dict('sys.modules', {'IPython': None})
+    def test_shell_with_ipython_not_installed(self, select):
+        select.return_value = ([], [], [])
+        with self.assertRaisesMessage(CommandError, "Couldn't import ipython interface."):
+            call_command('shell', interface='ipython')
+
+    @mock.patch('django.core.management.commands.shell.select.select')  # [1]
+    @mock.patch.dict('sys.modules', {'bpython': None})
+    def test_shell_with_bpython_not_installed(self, select):
+        select.return_value = ([], [], [])
+        with self.assertRaisesMessage(CommandError, "Couldn't import bpython interface."):
+            call_command('shell', interface='bpython')
+
+    # [1] Patch select to prevent tests failing when when the test suite is run
+    # in parallel mode. The tests are run in a subprocess and the subprocess's
+    # stdin is closed and replaced by /dev/null. Reading from /dev/null always
+    # returns EOF and so select always shows that sys.stdin is ready to read.
+    # This causes problems because of the call to select.select() towards the
+    # end of shell's handle() method.