从Python2升级到Python3时出现字符串/字节

Question

I try to generate base64 img of QRCode using Python 3 this way:

def gen_qrcode(data):
    import base64
    import io
    import qrcode

    qrc = qrcode.QRCode(version=1,
                        error_correction=qrcode.constants.ERROR_CORRECT_Q,
                        box_size=8,
                        border=4)
    qrc.add_data(data)
    qrc.make(fit=True)
    img = qrc.make_image()

    output = io.StringIO()
    img.save(output, 'PNG') # This line is now a problem with Python 3
    output.seek(0)
    output_s = output.read()
    b64 = base64.b64encode(output_s)
    img_tag = '<img src="data:image/png;base64,{0}">'.format(b64)

    return img_tag

It worked well with Python 2 (the only changed code is StringIO replaced by IO) but now I have an error:

TypeError at /qrcode
string argument expected, got 'bytes'
-> img.save(output, 'PNG')

Any idea? Thanks.

Answer 1

output = io.BytesIO

This will expect bytes and produce bytes for input to base64.b64encode.

To remove the leading "b" from the resulting output .decode() has to be used as mentioned in the comments:

b64 = base64.b64encode(output_s).decode()