hello,i have a quesion.i had completed opencv

cv2.error: /opt/conda/conda-bld/opencv_1491943704081/work/opencv-3.1.0/modules/calib3d/src/calibration.cpp:3314: error: (-215) nimages > 0 in function calibrateCamera

i meet a error, and this is why?what i should do?i made opencv, and seccessfully. i run main.py, this is wrong.