Question

I have an object that consists primarily of a very large nested dictionary:

class my_object(object):
    def __init__(self):
        self.the_dict = {}  # Big, nested dictionary

I’ve modified __ str__ to pretty-print the top-level dictionary by simply “printing” the object:

    def __str__(self):
        pp = pprint.PrettyPrinter()
        return pp.pformat(self.the_dict)

My goal here was to make the user’s life a bit easier when he/she peruses the object with IPython:

print(the_object)  # Pretty-prints entire dict

This works to show the user the entire dictionary, but I would like to expand this functionality to sub-portions of the dictionary as well, allowing the user to get pretty-printed output from commands such as:

print(the_object.the_dict['level1']['level2']['level3'])

(would pretty-print only the ‘level3’ sub-dict)

Is there a straight-forward way to use __ str__ (or similar) to do this?

Answer 1

You could provide a custom displayhook that prints builtin dictionaries and other objects you choose according to your taste at an interactive prompt:

>>> import sys
>>> oldhook = sys.displayhook
>>> sys.displayhook = your_module.DisplayHook(oldhook)

It doesn’t change print obj behavior.

The idea is that your users can choose whether they’d like to use your custom formatting for dicts or not.