Feat - Makes C0412 (ungrouped-imports) compatible with isort

Closes pylint-dev#2806.

CONTRIBUTORS.txt

@@ -285,3 +285,6 @@ contributors:
 * Bluesheeptoken: contributor
 
 * Michael Scott Cuthbert: contributor
+
+* Pierre Sassoulas : contributor
+    - Made C0412 (ungrouped import) compatible with isort

ChangeLog

@@ -56,6 +56,11 @@ Release date: TBA
 
   Close #2816
 
+* C0412 (ungrouped-import) is now compatible with isort.
+
+  Close #2806
+
+
 What's New in Pylint 2.3.0?
 ===========================
 

doc/whatsnew/2.4.rst

@@ -66,3 +66,15 @@ Other Changes
   command line. In addition to the ``--from-stdin`` flag a (single) file
   name needs to be specified on the command line, which is needed for the
   report.
+
+* The checker for ungrouped imports is now more permissive.
+
+The import can now be sorted alphabetically by import style.
+This makes pylint compatible with isort.
+
+This does not trigger a C0412 anymore and is OK ::
+
+    import unittest
+    import subprocess
+    from unittest import TestCase
+    from unittest.mock import MagicMock

pylint/checkers/imports.py

@@ -504,14 +504,19 @@ def leave_module(self, node):
         # Check imports are grouped by category (standard, 3rd party, local)
         std_imports, ext_imports, loc_imports = self._check_imports_order(node)
 
-        # Check imports are grouped by package within a given category
-        met = set()
+        # Check that imports are grouped by package within a given category
+        met_import = set()  #  set for 'import x' style
+        met_from = set()  #  set for 'from x import y' style
         current_package = None
         for import_node, import_name in std_imports + ext_imports + loc_imports:
             if not self.linter.is_message_enabled(
                 "ungrouped-imports", import_node.fromlineno
             ):
                 continue
+            if isinstance(import_node, astroid.node_classes.ImportFrom):
+                met = met_from
+            else:
+                met = met_import
             package, _, _ = import_name.partition(".")
             if current_package and current_package != package and package in met:
                 self.add_message("ungrouped-imports", node=import_node, args=package)

pylint/test/functional/ungrouped_imports.py

@@ -14,7 +14,13 @@
 from os import pardir
 import scipy
 from os import sep
-import astroid  # [ungrouped-imports]
+from astroid import exceptions # [ungrouped-imports]
 if True:
     import logging.handlers  # [ungrouped-imports]
 from os.path import join  # [ungrouped-imports]
+# Test related to compatibility with isort:
+# We check that we do not create error with the old way pylint was handling it
+import subprocess
+import unittest
+from unittest import TestCase
+from unittest.mock import MagicMock

pylint/test/functional/ungrouped_imports_isort_compatible.py

@@ -0,0 +1,6 @@
+"""Checks import order rule with imports that isort could generate"""
+# pylint: disable=unused-import
+import astroid
+import isort
+from astroid import are_exclusive, decorators
+from astroid.modutils import get_module_part, is_standard_module