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Add example of non-mutable mapping to cheat sheet #7620

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Merged
merged 4 commits into from
Oct 9, 2019
Merged

Add example of non-mutable mapping to cheat sheet #7620

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1faadc5
Add example of non-mutable mapping to cheat sheet
Oct 4, 2019
dcb232d
Merge branch 'master' of https://github.com/python/mypy into non-muta…
Oct 7, 2019
5fad6e1
Rewrite example
Oct 7, 2019
b769458
revert to original dict assignment
Oct 7, 2019
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3 changes: 2 additions & 1 deletion docs/source/cheat_sheet_py3.rst
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Expand Up @@ -212,12 +212,13 @@ that are common in idiomatic Python are standardized.
# Mapping describes a dict-like object (with "__getitem__") that we won't
# mutate, and MutableMapping one (with "__setitem__") that we might
def f(my_dict: Mapping[int, str]) -> List[int]:
my_mapping[5] = 'maybe' # if we try this, mypy will throw an error...
return list(my_dict.keys())

f({3: 'yes', 4: 'no'})

def f(my_mapping: MutableMapping[int, str]) -> Set[str]:
my_mapping[5] = 'maybe'
my_mapping[5] = 'maybe' # ...but mypy is OK with this.
return set(my_mapping.values())

f({3: 'yes', 4: 'no'})
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