Add is_colab() function (ultralytics#3018)

(cherry picked from commit fcd5702)

utils/general.py

@@ -51,11 +51,20 @@ def get_latest_run(search_dir='.'):
     return max(last_list, key=os.path.getctime) if last_list else ''
 
 
-def isdocker():
+def is_docker():
     # Is environment a Docker container
     return Path('/workspace').exists()  # or Path('/.dockerenv').exists()
 
 
+def is_colab():
+    # Is environment a Google Colab instance
+    try:
+        import google.colab
+        return True
+    except Exception as e:
+        return False
+
+
 def emojis(str=''):
     # Return platform-dependent emoji-safe version of string
     return str.encode().decode('ascii', 'ignore') if platform.system() == 'Windows' else str
@@ -84,7 +93,7 @@ def check_git_status():
     print(colorstr('github: '), end='')
     try:
         assert Path('.git').exists(), 'skipping check (not a git repository)'
-        assert not isdocker(), 'skipping check (Docker image)'
+        assert not is_docker(), 'skipping check (Docker image)'
         assert check_online(), 'skipping check (offline)'
 
         cmd = 'git fetch && git config --get remote.origin.url'
@@ -141,7 +150,8 @@ def check_img_size(img_size, s=32):
 def check_imshow():
     # Check if environment supports image displays
     try:
-        assert not isdocker(), 'cv2.imshow() is disabled in Docker environments'
+        assert not is_docker(), 'cv2.imshow() is disabled in Docker environments'
+        assert not is_colab(), 'cv2.imshow() is disabled in Google Colab environments'
         cv2.imshow('test', np.zeros((1, 1, 3)))
         cv2.waitKey(1)
         cv2.destroyAllWindows()