Resolved issue #1669: Parallel now defaults to number of CPU cores if…

… no value is provided

CHANGELOG.md

@@ -9,6 +9,7 @@ Find out more about isort's release policy [here](https://pycqa.github.io/isort/
   - Implemented #1648: Export MyPY type hints.
   - Implemented #1641: Identified import statements now return runnable code.
   - Implemented #1661: Added "wemake" profile.
+  - implemented #1669: Parallel (`-j`) now defaults to number of CPU cores if no value is provided.
 
 ### 5.7.0 December 30th 2020
   - Fixed #1612: In rare circumstances an extra comma is added after import and before comment.

isort/main.py

@@ -2,6 +2,7 @@
 import argparse
 import functools
 import json
+import multiprocessing
 import os
 import sys
 from gettext import gettext as _
@@ -268,7 +269,13 @@ def _build_arg_parser() -> argparse.ArgumentParser:
         help="Use the old deprecated finder logic that relies on environment introspection magic.",
     )
     general_group.add_argument(
-        "-j", "--jobs", help="Number of files to process in parallel.", dest="jobs", type=int
+        "-j",
+        "--jobs",
+        help="Number of files to process in parallel.",
+        dest="jobs",
+        type=int,
+        nargs="?",
+        const=multiprocessing.cpu_count(),
     )
     general_group.add_argument(
         "--ac",
@@ -844,6 +851,7 @@ def parse_args(argv: Optional[Sequence[str]] = None) -> Dict[str, Any]:
             arguments["multi_line_output"] = WrapModes(int(multi_line_output))
         else:
             arguments["multi_line_output"] = WrapModes[multi_line_output]
+
     return arguments