Dan's solution is just wrong, and Ismail's in incomplete.

1. __str__() is not called, __repr__() is called.
2. __repr__() should return a string, as pformat does.
3. print normally indents only 1 character and tries to save lines. If you are trying to figure out structure, set the width low and indent high.

Here is an example

class S:
    def __repr__(self):
        from pprint import pformat
        return pformat(vars(self), indent=4, width=1)

a = S()
a.b = 'bee'
a.c = {'cats': ['blacky', 'tiger'], 'dogs': ['rex', 'king'] }
a.d = S()
a.d.more_c = a.c

print(a)

This prints

{   'b': 'bee',
    'c': {   'cats': [   'blacky',
                         'tiger'],
             'dogs': [   'rex',
                         'king']},
    'd': {   'more_c': {   'cats': [   'blacky',
                               'tiger'],
                  'dogs': [   'rex',
                              'king']}}}

Which is not perfect, but passable.

While digging into pydantic's source code I found the devtools package, which solves this problem perfectly, as the doc described here

from datetime import datetime
from typing import List
from pydantic import BaseModel
from devtools import pprint

class Address(BaseModel):
    street: str
    country: str
    lat: float
    lng: float

class User(BaseModel):
    id: int
    name: str
    signup_ts: datetime
    friends: List[int]
    address: Address

user = User(
    id='123',
    name='John Doe',
    signup_ts='2019-06-01 12:22',
    friends=[1234, 4567, 7890],
    address=dict(street='Testing', country='uk', lat=51.5, lng=0),
)
pprint(user)

Output:

User(
    id=123,
    name='John Doe',
    signup_ts=datetime.datetime(2019, 6, 1, 12, 22),
    friends=[
        1234,
        4567,
        7890,
    ],
    address=Address(
        street='Testing',
        country='uk',
        lat=51.5,
        lng=0.0,
    ),
)

The pprint module has a function named pformat, for just that purpose.

From the documentation:

Return the formatted representation of object as a string. indent, width and depth will be passed to the PrettyPrinter constructor as formatting parameters.

Example:

>>> import pprint
>>> people = [
...     {"first": "Brian", "last": "Kernighan"}, 
...     {"first": "Dennis", "last": "Richie"},
... ]
>>> pprint.pformat(people, indent=4)
"[   {   'first': 'Brian', 'last': 'Kernighan'},\n    {   'first': 'Dennis', 'last': 'Richie'}]"