Add -rr/--reverse-relative option (issue #417)

This new option changes the sort order of relative imports. The new default
sort order is from furthest to closest (most dots to least dots):

    from ... import a
    from ...foo import x
    from .. import b
    from ..bar import y
    from . import c
    from .baz import z

With the new -rr/--reverse-relative option, the order of the relative
import *levels* (inter-order) is reversed, but the ordering within each
relative import level (intra-order) remains the same (i.e. normal lexical
order).

    from . import c
    from .baz import z
    from .. import b
    from ..bar import y
    from ... import a
    from ...foo import x

Signed-off-by: Peter Grayson <pete@jpgrayson.net>

4 files changed, 26 insertions, 8 deletions

diff --git a/isort/isort.py b/isort/isort.py
index ca28d56d..a763c92c 100644
--- a/isort/isort.py
+++ b/isort/isort.py
@@ -283,13 +283,10 @@ class SortImports(object):
         ignore_case: bool = False,
         section_name: Optional[Any] = None
     ) -> str:
-        dots = 0
-        while module_name.startswith('.'):
-            dots += 1
-            module_name = module_name[1:]
-
-        if dots:
-            module_name = '{} {}'.format(('.' * dots), module_name)
+        match = re.match(r'^(\.+)\s*(.*)', module_name)
+        if match:
+            sep = ' ' if config['reverse_relative'] else '_'
+            module_name = sep.join(match.groups())
 
         prefix = ""
         if ignore_case:
diff --git a/isort/main.py b/isort/main.py
index a2d4b935..80dbc712 100644
--- a/isort/main.py
+++ b/isort/main.py
@@ -253,6 +253,8 @@ def parse_args(argv: Optional[Sequence[str]] = None) -> Dict[str, Any]:
     parser.add_argument('-r', dest='ambiguous_r_flag', action='store_true')
     parser.add_argument('-rm', '--remove-import', dest='remove_imports', action='append',
                         help='Removes the specified import from all files.')
+    parser.add_argument('-rr', '--reverse-relative', dest='reverse_relative', action='store_true',
+                        help='Reverse order of relative imports.')
     parser.add_argument('-rc', '--recursive', dest='recursive', action='store_true',
                         help='Recursively look for Python files of which to sort imports')
     parser.add_argument('-s', '--skip', help='Files that sort imports should skip over. If you want to skip multiple '
diff --git a/isort/settings.py b/isort/settings.py
index c1d17802..815ed0a7 100644
--- a/isort/settings.py
+++ b/isort/settings.py
@@ -135,6 +135,7 @@ default = {'force_to_top': [],
            'length_sort': False,
            'add_imports': [],
            'remove_imports': [],
+           'reverse_relative': False,
            'force_single_line': False,
            'default_section': 'FIRSTPARTY',
            'import_heading_future': '',
diff --git a/test_isort.py b/test_isort.py
index b35d6cdd..cbc0ba00 100644
--- a/test_isort.py
+++ b/test_isort.py
@@ -2729,7 +2729,7 @@ def test_comments_not_removed_issue_576():
     assert SortImports(file_contents=test_input).output == test_input
 
 
-def test_inconsistent_relative_imports_issue_577():
+def test_reverse_relative_imports_issue_417():
     test_input = ('from . import ipsum\n'
                   'from . import lorem\n'
                   'from .dolor import consecteur\n'
@@ -2742,6 +2742,24 @@ def test_inconsistent_relative_imports_issue_577():
                   'from ... import dui\n'
                   'from ...eu import dignissim\n'
                   'from ...ex import metus\n')
+    assert SortImports(file_contents=test_input,
+                       force_single_line=True,
+                       reverse_relative=True).output == test_input
+
+
+def test_inconsistent_relative_imports_issue_577():
+    test_input = ('from ... import diam\n'
+                  'from ... import dui\n'
+                  'from ...eu import dignissim\n'
+                  'from ...ex import metus\n'
+                  'from .. import donec\n'
+                  'from .. import euismod\n'
+                  'from ..mi import iaculis\n'
+                  'from ..nec import tempor\n'
+                  'from . import ipsum\n'
+                  'from . import lorem\n'
+                  'from .dolor import consecteur\n'
+                  'from .sit import apidiscing\n')
     assert SortImports(file_contents=test_input, force_single_line=True).output == test_input