python TypeError: argument 1 must be string or read-only character buffer, not None

Question

Here is my code: def main():

    if len(sys.argv) != 3:

        fname = "OP.tex"
        dot_ind = fname.index(".") + 1
        ofname = fname[:dot_ind] + "1." + fname[dot_ind:]

    else:

        fname = sys.argv[1]
        ofname = sys.argv[2]
    print (fname, "+",ofname)
    writeout(ofname, replacement(readin(fname)))
def replacement(content):
   pattern = re.compile(r'(?<=\\\\\[-16pt]\n)([\s\S]*?)(?=\\\\\n\\thinhline)')
   re.findall(pattern, content)

if __name__ == "__main__":
    main()

For which I am receiving the following error:

File "test.py", line 30, in main
writeout(ofname, replacement(readin(fname)))
File "/home/utilities.py", line 138, in writeout
out.write(content)
TypeError: argument 1 must be string or read-only character buffer, not None

writeout is a function in another file that tells the python where to output the content as so:

def writeout(filename, content, append=False):
    """
    Writes content to file filename.
    """

    mode = "w"

    #append to the file instead of overwriting
    if append:
        mode = "a"

    #write content
    with open(filename, mode) as out:
        out.write(content)

The fname and ofname (input and output file names) are correct so why does the program say that the argument is None when it is a string?

Thank you so much.

Alex Martelli · Accepted Answer · 2015-01-02 15:05:58Z

6

Your replacement function must return a string and currently it returns None. So, change the statement

re.findall(pattern, content)

to something like

return ' '.join(re.findall(pattern, content))

Note you can't just return the result of re.findall, as that's a list, not a string; you must make a list out of that result, one way or another.

answered Jan 2, 2015 at 15:05

Alex Martelli

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