QR code generation failure for valid input

Question

I am trying to generate a custom QR code using the qrcode package, but I've run into an issue where it seems that it fails on valid input. I'm wondering if this is a bug in the package or expected behavior of a QR code that I'm not familiar with.

According to this site a version 1 QR code with Medium error correction can hold up to 20 alphanumeric values. Below myStr is a simple alphanumeric string that is 19 characters long and it fails with the output

qrcode.exceptions.DataOverflowError: Code length overflow. Data size (131) > size available (128)

However if I change myStr from 0000000000A0000A000 to 000000000000000A000, the string is still alphanumeric and still the same length, but then it passes.

import qrcode
qr = qrcode.QRCode(
    version=1,
    error_correction=qrcode.constants.ERROR_CORRECT_M,
)

myStr = '0000000000A0000A000'
print(len(myStr))
qr.add_data(myStr)
qr.make(fit=False)
img = qr.make_image()

Windows, Python 2.7, qrcode version 5.3, Pillow

Hao Li Hao Li · Accepted Answer · 2017-11-08T00:44:03

The error

qrcode.exceptions.DataOverflowError: Code length overflow. Data size (131) > size available (128)

is pointed to the buff which created by qrcode, not yours. In the qrcode/util.py:

print 'len(buffer):', len(buffer)
print 'buffer:', buffer
if len(buffer) > bit_limit:
    raise exceptions.DataOverflowError(
        "Code length overflow. Data size (%s) > size available (%s)" %
        (len(buffer), bit_limit))

The output about 0000000000A0000A000:

bit_limit: 128
len(buffer): 131
buffer: 16.40.0.0.0.0.64.20.17.1.0.0.32.33.194.0.0

The output about 000000000000000A000:

bit_limit: 128
len(buffer): 99
buffer: 16.60.0.0.0.0.0.0.32.33.194.0.0

You can use upper level version which has bigger bit_limit.

qr = qrcode.QRCode(
    version=2,      # use upper level version
    error_correction=qrcode.constants.ERROR_CORRECT_M,
)
> bit_limit: 224

QR code generation failure for valid input

2 Answers