With windows7, python2.7, opencv 3.0, the following works for me:

import cv2
import os

vvw = cv2.VideoWriter('mymovie.avi',cv2.VideoWriter_fourcc('X','V','I','D'),24,(640,480))
 
frameslist = os.listdir('.\\frames')
 
howmanyframes = len(frameslist)
 
print('Frames count: '+str(howmanyframes)) #just for debugging

for i in range(0,howmanyframes):
    print(i)
    theframe = cv2.imread('.\\frames\\'+frameslist[i])
    vvw.write(theframe)

With windows7, python2.7, opencv 3.0, the following works for me:

import cv2
import os

vvw           =   cv2.VideoWriter('mymovie.avi',cv2.VideoWriter_fourcc('X','V','I','D'),24,(640,480))
frameslist    =   os.listdir('.\\frames')
howmanyframes =   len(frameslist)
print('Frames count: '+str(howmanyframes)) #just for debugging

for i in range(0,howmanyframes):
    print(i)
    theframe = cv2.imread('.\\frames\\'+frameslist[i])
    vvw.write(theframe)