An attrs extension giving fields more control over how they're rendered in an autogenerated __repr__

attrs_flexible_repr.py

def attrs_flexible_repr(cls):
    
    """
    An [attrs](http://www.attrs.org/) extension giving attributes more
    flexibility about how they appear in the autogenerated `__repr__`.
    
    Out of the box, attrs gives your class a pretty decent `__repr__` method;
    you can disable this at the class level to define your own, or you can
    keep it but exclude attributes by setting their `repr` field to False.
    
    This extension adds to that by giving the attributes more control over
    how they're rendered, depending on the value of `repr` field; the new
    possibilities are:
    
    * `repr` a callable - pass the field's value to the callable and render
      its result as the value in the repr string.
      
    * `repr` a tuple - assumed to be a (str, callable) pair, where the str
      is the label to use for the attribute (rather than its name), and the
      callable is used as described above.
      
    (Otherwise it will just behave as usual.)
    
    Note that if you use this extension and also specify repr=False at the
    class level, that will be ignored: you _will_ get a __repr__ and any
    that you define for yourself will be ignored.
    
    Example:
    
    >>> @attrs_flexible_repr
    >>> @attr.s(repr=False)  # repr=False here ignored
    >>> class Example:
    >>>     username = attr.ib()  # Rendered as normal
    >>>     password = attr.ib(repr=False)  # Excluded from repr as normal
    >>>     # Next field is assumed to be a datetime.datetime
    >>>     time = attr.ib(repr=lambda t: t.isoformat(timespec='seconds'))
    >>>     content = attr.ib(repr=('Length', lambda c: len(c)))  # Title tweak
    >>>     weird = attr.ib(repr=lambda _: False)  # Always renders 'False'
    >>>
    >>> e = Example('me', 'xxx', datetime.datetime.now(), 'Hello there', 'Blah')
    >>> e
    Example(username=me, time=2018-06-15T10:52:13, Length=11, weird=False)

    """
    def flexible_repr(self):
        parts = []
        for field in cls.__attrs_attrs__:
            if not field.repr:
                continue
            field_name = field.name
            field_repr_callable = None
            field_value = getattr(self, field.name)
            if callable(field.repr):
                field_repr_callable = field.repr
            elif isinstance(field.repr, tuple):
                field_name, field_repr_callable = field.repr
            if field_repr_callable:
                field_value = field_repr_callable(field_value)
            parts.append('{}={}'.format(field_name, field_value))
        return '{}({})'.format(self.__class__.__name__, ', '.join(parts))

    cls.__repr__ = flexible_repr
    return cls

Note that attrs PR 568 makes this redundant, and is surely better implemented (see issue 212 there).