write()-ing an encoded string in Python 3.x

Question

I've got a unicode string (s) which I want to write into a file.

In Python 2 I could write:

open('filename', 'w').write(s.encode('utf-8'))

But this fails for Python 3. Apparently, s.encode() returns something of type 'bytes', which the write() function does not accept:

TypeError: must be str, not bytes

Does anyone know how to port the above code to Python 3?

Edit:

Thanks to all of you who proposed using binary mode! Unfortunately, this causes a problem with the \n characters. Is there any way to achieve the same result I had with Python 2 (namely to encode non-ANSI characters in UTF-8 while keeping the OS-specific rendition of \n)?

Thanks!

Answer 1

You do not want to muck around with manually encoding each and every piece of data like that! Simply pass the encoding as an argument to open, like this:

#!/usr/bin/env python3.2

slist = [
    "Ca\N{LATIN SMALL LETTER N WITH TILDE}on City",
    "na\N{LATIN SMALL LETTER I WITH DIAERESIS}vet\N{LATIN SMALL LETTER E WITH ACUTE}",
    "fa\N{LATIN SMALL LETTER C WITH CEDILLA}ade",
    "\N{GREEK SMALL LETTER BETA}-globulin"
]

with open("/tmp/sample.utf8", mode="w", encoding="utf8") as f:
    for s in slist:
        print(s, file=f)

Now if you the file you made, you’ll see that it says:

$ cat /tmp/sample.utf8
Cañon City
naïveté
façade
β-globulin

And you can see that those are the right code points this way:

$ uniquote -x /tmp/sample.utf 
Ca\x{F1}on City
na\x{EF}vet\x{E9}
fa\x{E7}ade
\x{3B2}-globulin

See how much easier that is? Let the stream object handle any low-level encoding or decoding for you.

Summary: Don't call encode or decode yourself when all you are doing is using them to process a homogeneous stream that's all of it in the same encoding. That's way too much bother for zero gain. Use the encoding argument just once and for all.