Add separate_packages option

docs/configuration/options.md

@@ -1039,6 +1039,59 @@ If `True` isort will automatically create section groups by the top-level packag
 **Python & Config File Name:** group_by_package  
 **CLI Flags:** **Not Supported**
 
+## Separate Packages
+
+Separate packages within the listed sections with newlines.
+
+**Type:** List of Strings  
+**Default:** `frozenset()`  
+**Config default:** `[]`  
+**Python & Config File Name:** separate_packages  
+**CLI Flags:** **Not Supported**
+
+**Examples:**
+
+### Example `.isort.cfg`
+
+```
+[settings]
+separate_packages=THIRDPARTY
+```
+
+### Example `pyproject.toml`
+
+```
+[tool.isort]
+separate_packages = ["THIRDPARTY"]
+```
+
+### Example before:
+```python
+import os
+import sys
+
+from django.db.models.signals import m2m_changed
+from django.utils import functional
+from django_filters import BooleanFilter
+from junitparser import JUnitXml
+from loguru import logger
+```
+
+### Example after:
+```python
+import os
+import sys
+
+from django.db.models.signals import m2m_changed
+from django.utils import functional
+
+from django_filters import BooleanFilter
+
+from junitparser import JUnitXml
+
+from loguru import logger
+```
+
 ## Ignore Whitespace
 
 Tells isort to ignore whitespace differences when --check-only is being used.

isort/output.py

@@ -8,6 +8,7 @@
 from . import parse, sorting, wrap
 from .comments import add_to_line as with_comments
 from .identify import STATEMENT_DECLARATIONS
+from .place import module_with_reason
 from .settings import DEFAULT_CONFIG, Config
 
 
@@ -149,6 +150,9 @@ def sorted_imports(
                     section_output.append("")  # Empty line for black compatibility
                     section_output.append(section_comment_end)
 
+            if section in config.separate_packages:
+                section_output = _separate_packages(section_output, config)
+
             if pending_lines_before or not no_lines_before:
                 output += [""] * config.lines_between_sections
 
@@ -674,3 +678,37 @@ def _with_star_comments(parsed: parse.ParsedContent, module: str, comments: List
     if star_comment:
         return [*comments, star_comment]
     return comments
+
+
+def _separate_packages(section_output: List[str], config: Config) -> List[str]:
+    group_keys: Set[str] = set()
+    comments_above: List[str] = []
+    processed_section_output: List[str] = []
+
+    for section_line in section_output:
+        if section_line.startswith("#"):
+            comments_above.append(section_line)
+            continue
+
+        package_name: str = section_line.split(" ")[1]
+        _, reason = module_with_reason(package_name, config)
+
+        if "Matched configured known pattern" in reason:
+            package_depth = len(reason.split(".")) - 1  # minus 1 for re.compile
+            key = ".".join(package_name.split(".")[: package_depth + 1])
+        else:
+            key = package_name.split(".")[0]
+
+        if key not in group_keys:
+            if group_keys:
+                processed_section_output.append("")
+
+            group_keys.add(key)
+
+        if comments_above:
+            processed_section_output.extend(comments_above)
+            comments_above = []
+
+        processed_section_output.append(section_line)
+
+    return processed_section_output

isort/settings.py

@@ -201,6 +201,7 @@ class _Config:
     force_sort_within_sections: bool = False
     lexicographical: bool = False
     group_by_package: bool = False
+    separate_packages: FrozenSet[str] = frozenset()
     ignore_whitespace: bool = False
     no_lines_before: FrozenSet[str] = frozenset()
     no_inline_sort: bool = False

tests/unit/test_ticketed_features.py

@@ -1073,3 +1073,111 @@ def use_libc_math():
 """,
         show_diff=True,
     )
+
+
+def test_sort_separate_packages_issue_2104():
+    """
+    Test to ensure that packages within a section can be separated by blank lines.
+    See: https://github.com/PyCQA/isort/issues/2104
+    """
+
+    # Base case as described in issue
+    assert (
+        isort.code(
+            """
+import os
+import sys
+
+from django.db.models.signals import m2m_changed
+from django.utils import functional
+from django_filters import BooleanFilter
+from junitparser import JUnitXml
+from junitparser import TestSuite
+from loguru import logger
+""",
+            force_single_line=True,
+            separate_packages=["THIRDPARTY"],
+        )
+        == """
+import os
+import sys
+
+from django.db.models.signals import m2m_changed
+from django.utils import functional
+
+from django_filters import BooleanFilter
+
+from junitparser import JUnitXml
+from junitparser import TestSuite
+
+from loguru import logger
+"""
+    )
+
+    # Check that multiline comments aren't broken up
+    assert (
+        isort.code(
+            """
+from junitparser import TestSuite
+# Some multiline
+# comment
+from loguru import logger
+""",
+            force_single_line=True,
+            separate_packages=["THIRDPARTY"],
+        )
+        == """
+from junitparser import TestSuite
+
+# Some multiline
+# comment
+from loguru import logger
+"""
+    )
+
+    # Check it works for custom sections
+    assert (
+        isort.code(
+            """
+import os
+from package2 import bar
+from package1 import foo
+            """,
+            force_single_line=True,
+            known_MYPACKAGES=["package1", "package2"],
+            sections=["STDLIB", "MYPACKAGES"],
+            separate_packages=["MYPACKAGES"],
+        )
+        == """
+import os
+
+from package1 import foo
+
+from package2 import bar
+"""
+    )
+
+    # Check it works for packages with deeper nesting
+    assert (
+        isort.code(
+            """
+import os
+from package2 import bar
+from package1.a.b import foo
+from package1.a.c import baz
+            """,
+            force_single_line=True,
+            known_MYPACKAGES=["package1.a", "package2"],
+            sections=["STDLIB", "MYPACKAGES"],
+            separate_packages=["MYPACKAGES"],
+        )
+        == """
+import os
+
+from package1.a.b import foo
+
+from package1.a.c import baz
+
+from package2 import bar
+"""
+    )