For non inlplace dict setdefault

dict_setdefault.py

"""
For non inlplace dict setdefault.
"""
base_dict = {'a': 'a-ORIG', 'b': 'b-ORIG', 'd': 'd-ORIG'}
defaults = {'a': 'A', 'b': None, 'c': 0}
overrides = defaults

# Update by override. Like: 
# - base_dict.update(overrides) -> new dict BUT `dict.update` is inplace
# - base_dict + overrides -> new dict BUT unsupported operand
print(dict(base_dict, **overrides))  # update by override i.e. 
{'a': 'A', 'b': None, 'c': 0, 'd': 'd-ORIG'}

# Update by setdefault. Like:
# - base_dict.set_defaults(defaults) -> new dict BUT there is only inplace `dict.setdefault`
# - defaults.update(base_dict) -> new dict  BUT `dict.update` is inplace
# - base_dict | defaults -> new dict BUT unsupported operand
print(dict(defaults, **base_dict))
{'a': 'a-ORIG', 'b': 'b-ORIG', 'c': 0, 'd': 'd-ORIG'}

# SUMMARY (only by literals, no dedicated method[s] ...)
# - py2+py3: dict(base_dict, **overrides) or dict(defaults, **base_dict)
# - py3 (>=3.5):  {**base_dict, **overrides} or {**defaults, **base_dict}