TypeError: write() argument must be str, not byte , upgrade to python 3 [duplicate]

Question

I am trying to upgrade my code to python 3. Having some trouble with this line,

output_file = open(working_dir + "E"+str(s)+".txt", "w+")

output_file.write(','.join(headers) + "\n")

and get this error TypeError: sequence item 0: expected str instance, bytes found

What i've tried,

  output_file.write(b",".join(headers) + b"\n")

TypeError: write() argument must be str, not bytes

ive also tried using decode() on the join, also tried using r and w+b on open.

How can i convert to str in python 3?

of what type is your variable values? b"" seems not appropriate here since write expects a str, not byte (as the error says) — FObersteiner
– FObersteiner, Commented Jul 29, 2019 at 14:42

FObersteiner · Accepted Answer · 2019-08-10 09:26:10Z

5

+50

EDIT: to read on how to convert bytes to string, follow the link provided by Martijn Pieters in the 'duplicate' tag.

my original suggestion

output_file.write(','.join([str(v) for v in values]) + "\n")

would give for example

values = [b'a', b'b', b'c']
print(','.join([str(v) for v in values]))
# b'a',b'b',b'c'

So despite this works, it might not be desired. If the bytes should be decoded instead, use bytes.decode() (ideally also with the appropriate encoding provided, for example bytes.decode('latin-1'))

values = [b'a', b'b', b'c']
print(','.join([v.decode() for v in values]))
# a,b,c

edited Aug 10, 2019 at 9:26

answered Jul 29, 2019 at 14:45

FObersteiner

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6 Comments

excelguy Over a year ago

Seems to work, a mistake in my question : I had "values" in my code, not "headers"

FObersteiner Over a year ago

so you still can't write the headers variable? Or is it all working now?

excelguy Over a year ago

it working, thank you.

Martijn Pieters Over a year ago

This is not how you decode bytes values though. You concatenated b'....' strings, the repr() representations. Instead, use bytes.decode().

FObersteiner Over a year ago

@MartijnPieters, thanks for the comment. I made an edit to clarify on that - although the question does not ask explicitly for decoding, it is most likely the desired procedure.

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