preview_decorator.py

def add_preview_for(*fields):
    """
    This is a decorator for model classes that adds preview methods.

    So instead of manually adding preview methods:
    
    >>> class Student(models.Model):
    ...     photo = models.ImageField()
    ...     icon = models.ImageField()
    ...
    ...     def preview_photo(self):
    ...         if not self.photo:
    ...             return '(no photo)'
    ...         return u'<img src="{}" />'.format(self.photo.url)
    ...
    ...     def preview_icon(self):
    ...         if not self.icon:
    ...             return '(no icon)'
    ...         return u'<img src="{}" />'.format(self.icon.url)

    You just can use this decorator with the same result:
    
    >>> @add_preview_for('photo', 'icon')
    ... class Student(models.Model):
    ...     photo = models.ImageField()
    ...     icon = models.ImageField()

    """
    html = u'<img src="{}" style="max-width: 100px; max-height: 100px" />'
    def make_method(field_name):
        method_name = '{}_preview'.format(field_name)
        def method(self):
            field = getattr(self, field_name)
            if not field:
                return '(no {})'.format(field_name)
            return html.format(field.url)
        method.short_description = '{} preview'.format(field_name.capitalize())
        method.allow_tags = True
        method.__name__ = str(method_name)
        return method_name, method

    def decorator(cls):
        for field_name in fields:
            method_name, method = make_method(field_name)
            setattr(cls, method_name, method)
        return cls

    return decorator