What is the python way to define a (non-class) type like:
typedef Dict[Union[int, str], Set[str]] RecordType
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In what context - do you want to define a new type that you can then use for type hints?Grismar– Grismar2021-10-05 07:10:54 +00:00Commented Oct 5, 2021 at 7:10
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GenericAliassahasrara62– sahasrara622021-10-05 07:14:17 +00:00Commented Oct 5, 2021 at 7:14
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2 Answers
This would simply do it?
from typing import Dict, Union, Set
RecordType = Dict[Union[int, str], Set[str]]
def my_func(rec: RecordType):
pass
my_func({1: {'2'}})
my_func({1: {2}})
This code will generate a warning from your IDE on the second call to my_func, but not on the first. As @sahasrara62 indicated, more here https://docs.python.org/3/library/stdtypes.html#types-genericalias
Since Python 3.9, the preferred syntax would be:
from typing import Union
RecordType = dict[Union[int, str], set[str]]
The built-in types can be used directly for type hints and the added imports are no longer required.
Since Python 3.10, the preferred syntax is
RecordType = dict[int | str, set[str]]
The | operator is a simpler way to create a union of types, and the import of Union is no longer required.
Since Python 3.12, the preferred syntax is
type RecordType = dict[int | str, set[str]]
The type keyword explicitly indicates that this is a type alias.
1 Comment
chubercik
I love how elegant and easy to understand Python's syntax is
In case users look for a distinct nominal typedef:
from typing import Dict, Union, Set, NewType
RecordType = Dict[Union[int, str], Set[str]]
DistinctRecordType = NewType("DistinctRecordType", Dict[Union[int, str], Set[str]])
def foo(rec: RecordType):
pass
def bar(rec: DistinctRecordType):
pass
foo({1: {"2"}})
bar(DistinctRecordType({1: {"2"}}))
bar({1: {"2"}}) # <--- this will cause a type error
This snippet demonstrates that only explicit casting will do.
$ mypy main.py
main.py:14: error: Argument 1 to "bar" has incompatible type "Dict[int, Set[str]]"; expected "DistinctRecordType"
Found 1 error in 1 file (checked 1 source file)