Update sys.path.append(str(ROOT)) (#4852)

* Update `sys.path.append(str(ROOT))`

* Cleanup

detect.py

@@ -16,7 +16,9 @@ import torch
 import torch.backends.cudnn as cudnn
 
 FILE = Path(__file__).resolve()
-sys.path.append(FILE.parents[0].as_posix())  # add yolov5/ to path
+ROOT = FILE.parents[0]  # YOLOv5 root directory
+if str(ROOT) not in sys.path:
+    sys.path.append(str(ROOT))  # add ROOT to PATH
 
 from models.experimental import attempt_load
 from utils.datasets import LoadImages, LoadStreams
@@ -284,7 +286,7 @@ def parse_opt():
 
 
 def main(opt):
-    check_requirements(exclude=('tensorboard', 'thop'))
+    check_requirements(requirements=ROOT / 'requirements.txt', exclude=('tensorboard', 'thop'))
     run(**vars(opt))