TypeError: sequence item 0: expected str instance, bytes found

Question

for line in fo:
    line = " ".join(line.split())
    line = line.strip()

I am getting an error

line = ''.join(line.split())
TypeError: sequence item 0: expected str instance, bytes found

its working fine in python 2.x, but not working on 3.4 kindly suggest a proper solution for that

Answer 1

' ' is a string which you're calling its join method with a byte sequence. As the documentation's stated, in python-3.x:

str.joinReturn a string which is the concatenation of the strings in the iterable iterable. A TypeError will be raised if there are any non-string values in iterable, including bytes objects. The separator between elements is the string providing this method.

But in this case since you are dealing with byte objects you cannot use str related methods. The byte object itself comes with a join() method that can be used in the same manner as str.join. You can also use io.BytesIO, or you can do in-place concatenation with a bytearray object. As the documentation's mentioned bytearray objects are mutable and have an efficient overallocation mechanism.

So you can simply add a b prefix to the empty string to make it a byte object:

line = b" ".join(line.split())

Also, if your file is contain strings you can simply open your file in a str mode ('r')instead of byte ('rb').

with open("input.txt", "r") as f:
    # Do something with f

---

Note that despite the separation between str and byte objects in python-3.x, in python-2.x you only have str. You can see this by checking the type of a string with b prefix:

In [2]: type(b'')
Out[2]: str

And that's what that makes the following snippet work:

"".join([b'www', b'www'])