Update dependency attrs to v20.3.0

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This PR contains the following updates:

Package	Type	Update	Change
attrs (source, changelog)	packages	minor	==20.1.0 -> ==20.3.0

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Release Notes

python-attrs/attrs

v20.3.0

Compare Source

Backward-incompatible Changes

• attr.define(), attr.frozen(), attr.mutable(), and attr.field() remain provisional.

  This release does not change anything about them and they are already used widely in production though.

  If you wish to use them together with mypy, you can simply drop this plugin into your project.

  Feel free to provide feedback to them in the linked issue #​668.

  We will release the attrs namespace once we have the feeling that the APIs have properly settled.
  #​668

Changes

• attr.s() now has a field_transformer hook that is called for all Attributes and returns a (modified or updated) list of Attribute instances.
  attr.asdict() has a value_serializer hook that can change the way values are converted.
  Both hooks are meant to help with data (de-)serialization workflows.
  #​653
• kw_only=True now works on Python 2.
  #​700
• raise from now works on frozen classes on PyPy.
  #​703,
  #​712
• attr.asdict() and attr.astuple() now treat frozensets like sets with regards to the retain_collection_types argument.
  #​704
• The type stubs for attr.s() and attr.make_class() are not missing the collect_by_mro argument anymore.
  #​711

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v20.2.0

Compare Source

Backward-incompatible Changes

• attr.define(), attr.frozen(), attr.mutable(), and attr.field() remain provisional.

  This release fixes a bunch of bugs and ergonomics but they remain mostly unchanged.

  If you wish to use them together with mypy, you can simply drop this plugin into your project.

  Feel free to provide feedback to them in the linked issue #​668.

  We will release the attrs namespace once we have the feeling that the APIs have properly settled.
  #​668

Changes

• attr.define() et al now correctly detect __eq__ and __ne__.
  #​671

• attr.define() et al's hybrid behavior now also works correctly when arguments are passed.
  #​675

• It's possible to define custom __setattr__ methods on slotted classes again.
  #​681

• In 20.1.0 we introduced the inherited attribute on the attr.Attribute class to differentiate attributes that have been inherited and those that have been defined directly on the class.

  It has shown to be problematic to involve that attribute when comparing instances of attr.Attribute though, because when sub-classing, attributes from base classes are suddenly not equal to themselves in a super class.

  Therefore the inherited attribute will now be ignored when hashing and comparing instances of attr.Attribute.
  #​684

• zope.interface is now a "soft dependency" when running the test suite; if zope.interface is not installed when running the test suite, the interface-related tests will be automatically skipped.
  #​685

• The ergonomics of creating frozen classes using @define(frozen=True) and sub-classing frozen classes has been improved:
  you don't have to set on_setattr=None anymore.
  #​687

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