Question

I’m writing the following function to format some text from a file object ‘item’:

def clean(item):
    lines = open(str(item)).readlines()
    outp = []
    switch = 1

    for line in lines:
        line = line.strip()
        if line:
            line = re.sub(' +', ' ', line)
            if '%' in line:
                line = line.replace('%', ' per cent')
            if line.startswith('Note'):
                switch = 2

            if line.startswith('l\t'):
                line = line.split('\t')
                line[0] = '<@01_bullet_point>l<@$p>'
                line = '\t'.join(line)
                outp.append(get_prefix(switch,1) + line)
            else:
                outp.append(get_prefix(switch,2) + line)
            outp.append('\n')
    return ''.join(outp)

I’m getting a TypeError: unsupported operand types for +: ‘NoneType’ and ‘str’

I googled around for solutions but found http://www.skymind.com/~ocrow/python_string/, whose solution 4 seemed to confirm that I was on the right track.

The other function(s) this is referencing are confirmed working so I know the problem must be in here but, having tried to find related SO questions and checked my copy of Python in a Nutshell, I can’t figure out why I’m getting the error. My best guess was something to do with variable scope but I can’t see it and, again, searching turned up nothing I could understand as the same problem. I expect I’m missing something obvious but any help would be much appreciated.

EDIT
get_prefix is:

def get_prefix(section, type):
    if section == 1:
        if type == 1:
            prefix = '@01_bullets:'
        elif type == 2:
            prefix = '@04_section_sub_subhead:'
        else:
            prefix = '@06_body_text:'

    else:
        if type == 2:
            prefix = '@14_notes_sub_sub_heading:'
        else:
            prefix = '@16_notes_text:'

    return prefix

I can’t see how it might return None.

The full traceback is:

File "rep_builder.py", line 65, in <module>
`rep.write(clean(item))`
File "rep_builder.py", line 36, in clean
`outp.append(get_prefix(switch,2) + line)`
TypeError: unsupported operand types for +: 'NoneType' and 'str'

Sorry for slow updates I’m working across two unconnectable machines (long story).

Answer 1

Check your indentation. Are you sure get_prefix doesn’t look something like this? (I ask because the indentation in clean is wrong):

def get_prefix(section, type):
    if section == 1:
        if type == 1:
            prefix = '@01_bullets:'
        elif type == 2:
            prefix = '@04_section_sub_subhead:'
        else:
            prefix = '@06_body_text:'

    else:
        if type == 2:
            prefix = '@14_notes_sub_sub_heading:'
        else:
            prefix = '@16_notes_text:'

        return prefix

Indented as above, get_prefix will return None if section equals 1.