my_dict = {}
default_value = {'surname': '', 'age': 0}

# get info about john, or a default dict
item = my_dict.get('john', default_value)

# edit the data
item[surname] = 'smith'
item[age] = 68

my_dict['john'] = item

>>> default_value
{'age': 68, 'surname': 'smith'}

item = my_dict.get('john', {'surname': '', 'age': 0})

item = my_dict.get('john', default_value.copy())

def my_dict_get(key):
    try:
        item = my_dict[key]
    except KeyError:
        item = default_value.copy()

my_dict.get('john', default_value.copy())

from collections import defaultdict

def factory():
  return {'surname': '', 'age': 0}

my_dict = defaultdict(factory)

my_dict['john']

item = my_dict.get('john', default_value.copy())

item = my_dict['john'] if 'john' in my_dict else default_value.copy()

item = my_dict.get('john')
if item is None:
    item = default_value.copy()

def my_dict_get():
    try:
        item = my_dict['key']
    except KeyError:
        item = default_value.copy()

# key present: 0.4179
# key absent: 3.3799

def my_dict_get():
    item = my_dict.get('key')
    if item is None:
        item = default_value.copy()

# key present: 0.57189
# key absent: 0.96691

def my_dict_get():
    item = my_dict['key'] if 'key' in my_dict else default_value.copy()

# key present: 0.39721
# key absent: 0.43474

def my_dict_get():
    item = my_dict.get('key', default_value.copy())

# key present: 0.52303 (this may be lower than it should be as the dictionary I used was one element)
# key absent: 0.66045

item = my_dict.get('john')
if item is None:
    item = default_dict.copy()

try:
    return my_dict['john']
except KeyError:
    return {'surname': '', 'age': 0}

import collections

def default_factory():
    return {'surname': '', 'age': 0}

my_dict = collections.defaultdict(default_factory)