Okay, I think the error message can be improved because in Python 2.7 we differentiate very clearly the string from the unicode.

>>> import struct
>>> struct.Struct(1)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: Struct() argument 1 must be string, not int

But you can give unicode, right?

>>> struct.Struct(u'b')
<Struct object at 0x1f484b8>

This is consistent with other example:

>>> " cutecat ".strip(1)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: strip arg must be None, str or unicode

What do you say, Serhiy?

Here is the patch.