Question

I’ve got a very strange problem with python-qrcode.

I’ve had it working in our dev environment for a while now, without any issues. We use it to create two QR codes both of which contain URLs of almost exactly the same length (one contains an extra letter and two extra slashes). It’s crucial that these two codes be exactly the same size.

Since we setup python-qrcode about five months ago, every single qrcode we have generated has been exactly the same size without fail. However, we’ve now pushed everything through to a production server and suddenly we have a problem.

Basically, one of the codes we generate is bigger than normal (this is the one with the three extra characters). The other code is the correct size. The two codes are generated using exactly the same function, we just pass the different URL to be encoded.

On my local machine and on our dev server, all the qrcodes are exactly the same size (including the one with the extra characters), but on the production server, the longer one is bigger while the other is correct.

We use Git version control, so all the files/functions etc are identical between the servers. The only difference between the setups is the version of Ubuntu (12.04 vs 12.10 on the production server), but I can’t see why that would cause this issue.

If both codes were bigger, I could understand, but I can’t work out why one would be bigger than the other on only one server…..?

If anyone can make any suggestion as to where to start working this out, I’d be very grateful!

EDIT:

Here’s the relevant code:

myQrGenerator = qrcode.QRCode(
    version=QRCODE_SIZE,
    error_correction=qrcode.constants.ERROR_CORRECT_M,
    box_size=QRCODE_BOX_SIZE,
    border=QRCODE_BORDER_SIZE
)

myQrGenerator.add_data('%s%s/' % (theBaseUrl, str(theHash)))
myQrGenerator.make(fit=True)

We get those variables from local_settings.py

Answer 1

After a lengthy discussion it was established that the two servers used different URLs. The one that spewed out a larger QR code (in terms of QR pixels, and subsequently in terms of image pixels) overflowed, where the limit of bits it could store for the predefined size was not enough, and qrcode made it fit by increasing the amount of data it could store.

To fix this, fit was set False to provide a constraint for overflows, and version was increased to accomodate more bits from the start. box_size can be decreased a bit to maintain, more or less, the original image size.