csv: re-export Dialect from _csv #3613
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Resolves python#3611 Tested with mypy on: ``` f = open("asdf.csv", "w") csv.writer(f) csv.writer(f, dialect=csv.excel) csv.writer(f, dialect=csv.excel()) csv.DictReader(f) csv.DictReader(f, dialect=csv.excel) csv.DictReader(f, dialect=csv.excel()) class CustomDialect(csv.Dialect): delimiter = "%" csv.writer(f, dialect=CustomDialect) csv.writer(f, dialect=CustomDialect()) ```
| _DictRow = Mapping[str, Any] | ||
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| class Dialect(object): |
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I thought this was actually an unrelated class at runtime? If so, we should probably keep it here, but accept both the _csv and the csv Dialects below.
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They are separate classes at runtime, but are perhaps morally one class, since all the CPython code duck types around it.
The issue is _csv.writer also needs to accept csv.Dialect so that common code like csv.writer(f, dialect=csv.excel) is accepted, as in #3611.
I guess we could get around the cyclic import with if TYPE_CHECKING? Does that work in pyi / is that better?
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Cyclic imports are supported in stubs. if TYPE_CHECKING is not necessary as it's implied.
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We discussed this some more; it seems best to just treat both as one class because that's how they're used in practice.
Resolves #3611
Tested with mypy on: