Python print isn't using __repr__, __unicode__ or __str__ for unicode subclass?

Question

Python print isn\'t using __repr__, __unicode__ or __str__ for my unicode subclass when printing. Any clues as to what I am doing wron

Answer 1

The problem is that print doesn't respect __str__ on unicode subclasses.

From PyFile_WriteObject, used by print:

int
PyFile_WriteObject(PyObject *v, PyObject *f, int flags)
{
...
        if ((flags & Py_PRINT_RAW) &&
    PyUnicode_Check(v) && enc != Py_None) {
    char *cenc = PyString_AS_STRING(enc);
    char *errors = fobj->f_errors == Py_None ? 
      "strict" : PyString_AS_STRING(fobj->f_errors);
    value = PyUnicode_AsEncodedString(v, cenc, errors);
    if (value == NULL)
        return -1;

PyUnicode_Check(v) returns true if v's type is unicode or a subclass. This code therefore writes unicode objects directly, without consulting __str__.

Note that subclassing str and overriding __str__ works as expected:

>>> class mystr(str):
...     def __str__(self): return "str"
...     def __repr__(self): return "repr"
... 
>>> print mystr()
str

as does calling str or unicode explicitly:

>>> class myuni(unicode):
...     def __str__(self): return "str"
...     def __repr__(self): return "repr"
...     def __unicode__(self): return "unicode"
... 
>>> print myuni()

>>> str(myuni())
'str'
>>> unicode(myuni())
u'unicode'

I believe this could be construed as a bug in Python as currently implemented.