Add install=True argument to check_requirements (ultralytics#4512)

* Add `install=True` argument to `check_requirements`

* Update general.py

utils/general.py

@@ -172,7 +172,7 @@ def check_version(current='0.0.0', minimum='0.0.0', name='version ', pinned=Fals
 
 
 @try_except
-def check_requirements(requirements='requirements.txt', exclude=()):
+def check_requirements(requirements='requirements.txt', exclude=(), install=True):
     # Check installed dependencies meet requirements (pass *.txt file or list of packages)
     prefix = colorstr('red', 'bold', 'requirements:')
     check_python()  # check python version
@@ -188,13 +188,17 @@ def check_requirements(requirements='requirements.txt', exclude=()):
         try:
             pkg.require(r)
         except Exception as e:  # DistributionNotFound or VersionConflict if requirements not met
-            print(f"{prefix} {r} not found and is required by YOLOv5, attempting auto-update...")
-            try:
-                assert check_online(), f"'pip install {r}' skipped (offline)"
-                print(check_output(f"pip install '{r}'", shell=True).decode())
-                n += 1
-            except Exception as e:
-                print(f'{prefix} {e}')
+            s = f"{prefix} {r} not found and is required by YOLOv5"
+            if install:
+                print(f"{s}, attempting auto-update...")
+                try:
+                    assert check_online(), f"'pip install {r}' skipped (offline)"
+                    print(check_output(f"pip install '{r}'", shell=True).decode())
+                    n += 1
+                except Exception as e:
+                    print(f'{prefix} {e}')
+            else:
+                print(f'{s}. Please install and rerun your command.')
 
     if n:  # if packages updated
         source = file.resolve() if 'file' in locals() else requirements