no matching distribution found for nltk pip code example

Example 1: ERROR: Could not find a version that satisfies the requirement cv2 (from versions: none) ERROR: No matching distribution found for cv2

#Know the reason is really dumb, because the reason is that the package of CV2 is not called cv2 but called opencv-python

pip install opencv-python

#For python3:
pip3 install opencv-python

Example 2: pip install tensorflow no matching distribution found for tensorflow

this error will show only on python 3.9 if you use python 3.8 or before and after python 3.5 or something you wont get this error