opencv cascade classifier no open palm detected

I have the following code which should detect a open palm in img.jpg:

    #!/usr/bin/env python
    # -*- coding: utf-8 -*-
    import cv2
    import glob
    

    #somehow if the path doesn't end in \n it will raise another error
    classifier=cv2.CascadeClassifier("path/to/classifier.xml\n")
    r=classifier.detectMultiScale(cv2.cvtColor(img,cv2.CV_8U))
    print r
    cv2.rectangle(img,r[0],r[1],(0,0,255))
    cv2.imshow("result",img)
    cv2.waitKey(1000)
classifier.xml is generated by a script similar to

    i="path/to/positives/images"
    cd $i
    #list of the positive images
    find . -name '*' -exec identify -format '%i 1 0 0 %w %h' \{\} \; >ls.txt
    opencv_createsamples -vec $(pwd)/coll.vec -info ls.txt \
        -bg negatives/ls.txt -w 24 -h 24 -num 1550
    mkdir path/to/classifiers #the directory where we put the classifiers

    opencv_traincascade -data path/to/classifiers\
        -bg negatives/ls.txt -vec coll.vec -featureType LBP \
        -w 24 -h 24 -numPos 1300 -minHitRate 0.99 \
        -precalcValBufSize 4096 -precalcIdxBufSize 4096
But when I execute the python script it gives me the following output
 
    ()
    Traceback (most recent call last):
      File "test1.py", line 13, in <module>
        cv2.rectangle(img,r[0],r[1],(0,0,255))
    IndexError: tuple index out of range
How and where did I do wrong?