[docs] Specify that unittest.mock.patch.dict does not make a deepcopy

[romuald]

Documentation

I always assumed that unittest.mock.patch.dict made a recursive (deep) copy of the dict and restored it afterwards.
It turns out it is a "simple" copy()

We should maybe clarify that in the documentation

Example:

foo = {
  "bar": {"baz": 1}
}

with patch.dict(foo, {"unrelated": 123}):
  foo["bar"]["baz"] = 2

# baz will stay at 2, assumed it was reset to the original 1

Linked PRs

• gh-144433: clarify unittest.mock.patch.dict copy behavior #144434

[serhiy-storchaka]

In your example you do not change the dictionary. You only change the object referred by a dictionary. You can test this -- set value = foo["bar"] before modification, and assert that foo["bar"] is value after modification. This is how Python's dicts work. This is how anything works in Python. This is an expected, standard behavior, and changing documentation will only confuse users.