[Python-ideas] automation of __repr__/__str__ for all the common simple cases

Nathan Rice nathan.alexander.rice at gmail.com
Wed Feb 15 16:34:45 CET 2012

I think that a generic __repr__ has been reinvented more times than I
can count.  I don't think a generic __str__ is a good thing, as it is
supposed to be a pretty, semantically meaningful.  I don't really see
anywhere in the standard library that such a feature would make sense
though.  I feel like Python's standard library bloat actually makes
the good stuff harder to find, and a better approach would be to have
a minimal "core" standard library with a few "official" battery pack
style libs that are very prominently featured and available.

Since you might find this useful, here is my old __repr__ reciple
(which has several issues, but gets the job done for the most part):

def get_attributes(o):
    attributes = [(a, getattr(o, a)) for a in
set(dir(o)).difference(dir(object)) if a[0] != "_"]
    return {a[0]: a[1] for a in attributes if not callable(a[1])}

class ReprMixin(object):

    def _format(self, v):
        if isinstance(v, (basestring, date, time, datetime)):
            v = "'%s'" % v
            return v.encode("utf-8", errors="ignore")
            return v

    def __repr__(self):
        attribute_string = ", ".join("%s=%s" % (k[0],
self._format(k[1])) for k in get_attributes(self).items())
        return "%s(%s)" % (type(self).__name__, attribute_string)

There is a similar recipes in SQL Alchemy, and I've seen them in a few
other popular libs that I can't remember off the top of my head.


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