Best output type and encoding practices for __repr__() functions?

In Python2, __repr__ (and __str__) must return a string object, not aunicode object. In Python3, the situation is reversed, __repr__ and __str__must return unicode objects, not byte (née string) objects:

class Foo(object):    def __repr__(self):        return u'\N{WHITE SMILING FACE}' class Bar(object):    def __repr__(self):        return u'\N{WHITE SMILING FACE}'.encode('utf8')repr(Bar())# ☺repr(Foo())# UnicodeEncodeError: 'ascii' codec can't encode character u'\u263a' in position 0: ordinal not in range(128)

In Python2, you don't really have a choice. You have to pick an encoding for thereturn value of __repr__.

By the way, have you read the PrintFails wiki? It may not directly answeryour other questions, but I did find it helpful in illuminating why certainerrors occur.

When using from __future__ import unicode_literals,

'<{}>'.format(repr(x).decode('utf-8'))).encode('utf-8')

can be more simply written as

str('<{}>').format(repr(x))

assuming str encodes to utf-8 on your system.

Without from __future__ import unicode_literals, the expression can be written as:

'<{}>'.format(repr(x))

I think a decorator can manage __repr__ incompatibilities in a sane way. Here's what i use:

from __future__ import unicode_literals, print_functionimport sysdef force_encoded_string_output(func):    if sys.version_info.major < 3:        def _func(*args, **kwargs):            return func(*args, **kwargs).encode(sys.stdout.encoding or 'utf-8')        return _func    else:        return funcclass MyDummyClass(object):    @force_encoded_string_output    def __repr__(self):        return 'My Dummy Class! \N{WHITE SMILING FACE}'

I use a function like the following:

def stdout_encode(u, default='UTF8'):    if sys.stdout.encoding:        return u.encode(sys.stdout.encoding)    return u.encode(default)

Then my __repr__ functions look like this:

def __repr__(self):    return stdout_encode(u'<MyClass {0} {1}>'.format(self.abcd, self.efgh))