Python 2 ordinal not in range on join - unicode

Question

When I do
u','.join([u'\u4e8c\u6797', unicode(10)])
it fails with UnicodeEncodeError: 'ascii' codec can't encode characters in position 0-1: ordinal not in range(128). All three items in the list are of type unicode.
Why is it trying to encode in ascii? I don't want it to convert to ascii string. How do I avoid it?

Answer 1

Not really enough information, since it works just fine as displayed:
>>> u','.join([u'\u4e8c\u6797', unicode(10)])
u'\u4e8c\u6797,10'
But my crystal ball says you are trying to print it in some manner:
>>> print u','.join([u'\u4e8c\u6797', unicode(10)])
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "D:\dev\Python27\lib\encodings\cp437.py", line 12, in encode
return codecs.charmap_encode(input,errors,encoding_map)
UnicodeEncodeError: 'charmap' codec can't encode characters in position 0-1: character maps to <undefined>
The reason is, at least on my system, is the terminal uses cp437 encoding and can't encode the Unicode characters in that encoding.
Or more likely writing to a file or pipe:
>>> with open('out.txt','w') as f:
... f.write(u','.join([u'\u4e8c\u6797', unicode(10)]))
...
Traceback (most recent call last):
File "<stdin>", line 2, in <module>
UnicodeEncodeError: 'ascii' codec can't encode characters in position 0-1: ordinal not in range(128)
Files have to be told the encoding, such as UTF-8, or they default to ASCII:
>>> import codecs
>>> with open('out.txt','w') as f:
... f.write(u','.join([u'\u4e8c\u6797', unicode(10)]).encode('utf8'))
...
>>> # SUCCESS!