What's the difference between cv and cv2 using python2?

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I've compiled OpenCV-2.4.6 on Windows machine and using Python2.7 to create OpenCV applications.

There lots of examples out there on the web but you can't use them right away and need to fix to make them run, because some of them use "cv", others use "cv2" or other packages. What's the main difference between import cv and import cv2 on python2? Is cv2 an extension to cv and you always must use cv2? Are there bigger amount of functions in cv2 but some of them are only in cv?

cv or cv2? or both?