code works on windows laptop but not on PI

Question

I'm calling this function on my laptop with (python version 2.72) and it works well; but when I move it to my PI (python ver 3.2.3) I get:

Traceback (most recent call last):
  File "/usr/src/scripts/areadetect_movie_pi_17.py", line 337, in <module>
    save_frame_deque(reduced, 10)
  File "/usr/src/scripts/areadetect_movie_pi_17.py", line 65, in save_frame_deque
    cv2.imwrite('/home/pi/Desktop/frame_2.jpg', q.popleft())
TypeError: <unknown> is not a numpy array

The code:

max_qlength = 10 
q = deque ([0,max_qlength]) 

    def save_frame_deque(picture, max_qlen):

        max_qlength = max_qlen

        q.append(picture)


        print(len(q))# actual length of que
        print (max_qlength)# max length of que

        if len(q) >  (max_qlength+1): # if actual length of q is bigger than 11

            #cv2.imwrite('/home/pi/Desktop/frame_1.jpg', picture)
            #cv2.imshow("frame", q.popleft())

            cv2.imwrite('/home/pi/Desktop/frame_2.jpg', q.popleft())
            cv2.imwrite('/home/pi/Desktop/frame_3.jpg', q.popleft())

            cv2.imwrite('/home/pi/Desktop/frame_4.jpg', q.popleft())
            cv2.imwrite('/home/pi/Desktop/frame_5.jpg', q.popleft())
            cv2.imwrite('/home/pi/Desktop/frame_6.jpg', q.popleft())
            cv2.imwrite('/home/pi/Desktop/frame_7.jpg', q.popleft())
            cv2.imwrite('/home/pi/Desktop/frame_8.jpg', q.popleft())
            cv2.imwrite('/home/pi/Desktop/frame_9.jpg', q.popleft())
            cv2.imwrite('/home/pi/Desktop/frame_10.jpg', q.popleft())
            cv2.imwrite('/home/pi/Desktop/frame_11.jpg', q.popleft())

when I change the code to:

    max_qlength = 10 
    q = deque ([0,max_qlength]) 

        def save_frame_deque(picture, max_qlen):

            max_qlength = max_qlen

            q.append(picture)


            print(len(q))# actual length of que
            print (max_qlength)# max length of que

            if len(q) >  (max_qlength+1): # if actual length of q is bigger than 11

                cv2.imwrite('/home/pi/Desktop/frame_1.jpg', picture)
                #cv2.imshow("frame", q.popleft())

                '''
                cv2.imwrite('/home/pi/Desktop/frame_2.jpg', q.popleft())
                cv2.imwrite('/home/pi/Desktop/frame_3.jpg', q.popleft())

                cv2.imwrite('/home/pi/Desktop/frame_4.jpg', q.popleft())
                cv2.imwrite('/home/pi/Desktop/frame_5.jpg', q.popleft())
                cv2.imwrite('/home/pi/Desktop/frame_6.jpg', q.popleft())
                cv2.imwrite('/home/pi/Desktop/frame_7.jpg', q.popleft())
                cv2.imwrite('/home/pi/Desktop/frame_8.jpg', q.popleft())
                cv2.imwrite('/home/pi/Desktop/frame_9.jpg', q.popleft())
                cv2.imwrite('/home/pi/Desktop/frame_10.jpg', q.popleft())
                cv2.imwrite('/home/pi/Desktop/frame_11.jpg', q.popleft())
                '''

it works, so this would appear that my pi doesn't like popleft()

1) Is this the case, i'm not sure how to check if popleft is available in Python 3.2.3? 2) How do I fix this? 3) if poleft isn't available in the newer version of python, then is there an equivalent? there an

Answer 1

Arr, what a fool I am!

I opened the Python shell on the PI and did this:

Python 3.2.3 (default, Mar  1 2013, 11:53:50) 
[GCC 4.6.3] on linux2
Type "copyright", "credits" or "license()" for more information.
>>> from collections import deque
>>> q = deque ([0,10])
>>> q.append("1a")
>>> q.append("2a")
>>> q.append("3a")
>>> print(q.popleft())
0
>>> print(q.popleft())
10
>>> print(q.popleft())
1a
>>> print(q.popleft())
2a
>>> print(q.popleft())
3a
>>> print(q.popleft())
Traceback (most recent call last):
  File "<pyshell#10>", line 1, in <module>
    print(q.popleft())
IndexError: pop from an empty deque
>>>

Which, to me, suggested that I needed to flush the first two values i'd loaded!

Following this example, I could see that following a popleft I got 0 then 10 then 1a, so it dawned on me that I was preloading the dque with 2 integers not numpy arrays.

so I modified my script to flush out the 2 pre loaded integers and it worked:

max_qlength = 10 
q = deque ([0,max_qlength]) 

    def save_frame_deque(picture, max_qlen):

        max_qlength = max_qlen

        q.append(picture)

        if len(q) >  (max_qlength+1):


            q.popleft()
            q.popleft()

            cv2.imwrite('/home/pi/Desktop/frame_2.jpg', q.popleft())
            cv2.imwrite('/home/pi/Desktop/frame_3.jpg', q.popleft())

            cv2.imwrite('/home/pi/Desktop/frame_4.jpg', q.popleft())
            cv2.imwrite('/home/pi/Desktop/frame_5.jpg', q.popleft())
            cv2.imwrite('/home/pi/Desktop/frame_6.jpg', q.popleft())
            cv2.imwrite('/home/pi/Desktop/frame_7.jpg', q.popleft())
            cv2.imwrite('/home/pi/Desktop/frame_8.jpg', q.popleft())
            cv2.imwrite('/home/pi/Desktop/frame_9.jpg', q.popleft())
            cv2.imwrite('/home/pi/Desktop/frame_10.jpg', q.popleft())
            cv2.imwrite('/home/pi/Desktop/frame_11.jpg', q.popleft())

Or a more elegant solution is not to load the integers in in the first place, define an empty deque, and specify the max_qlen when one calls the function!

q = deque ([])

def save_frame_deque(picture, max_qlen):

    q.append(picture)

    if (len(q)) >  (max_qlen): 

        cv2.imwrite('/home/pi/Desktop/frame_1.jpg', q.popleft())
        cv2.imwrite('/home/pi/Desktop/frame_2.jpg', q.popleft())
        cv2.imwrite('/home/pi/Desktop/frame_3.jpg', q.popleft())

        cv2.imwrite('/home/pi/Desktop/frame_4.jpg', q.popleft())
        cv2.imwrite('/home/pi/Desktop/frame_5.jpg', q.popleft())
        cv2.imwrite('/home/pi/Desktop/frame_6.jpg', q.popleft())
        cv2.imwrite('/home/pi/Desktop/frame_7.jpg', q.popleft())
        cv2.imwrite('/home/pi/Desktop/frame_8.jpg', q.popleft())
        cv2.imwrite('/home/pi/Desktop/frame_9.jpg', q.popleft())
        cv2.imwrite('/home/pi/Desktop/frame_10.jpg', q.popleft())
        cv2.imwrite('/home/pi/Desktop/frame_11.jpg', q.popleft())

when the count (len(q)) > (max_qlen) becomes true (when len(q) == 13) the program running on the laptop empties the deque, saving the first two jpgs with the number ten, hence corrupt jpgs; whereas the PI complains with the already highlighted error.

see the eclipse screensot of when len(q) == 13:

and the resultant jpg output of an integer of value 10:

I'm assuming eclipse doesn't complain when you ask it to convert the number 10 to a jpg, but the PI does!

Answer 2

Python 3 is not backward compatible. Code written in one version will have to be ported to the other. You can not expect that code developed in Python 2 to be runnable in Python 3, or the other way around. See to that your development environment and your production environment run the same version on Python, down to the last decimal.