This code is originally based on Abid Rahman K's answer in Simple Digit Recognition OCR in OpenCV-Python.

Several tiny modification has been made to adapt OpenCV's new API.

Hope it helps for OpenCV newbies.

Run train.py, label the number surrounded with red rectangle manually. The labeled result will seems like

Run test.py, the program will load the test image and automatically recognize digits using KNearNeighbour Algorithm. The results will seem like

Labeled Test Image

Recognized Digits

>>> sys.version
'2.7.10 |Anaconda 2.3.0 (64-bit)| (default, May 28 2015, 16:44:52) [MSC v.1500 64 bit (AMD64)]'

>>> numpy.__version__
'1.9.2'

>>> cv2.__version__
'3.0.0'