dataclas 0.9.3

Slightly improved dataclasses, backward compatible

• dataclass: like dataclasses.dataclass, except:

  • Adds three new instance methods to each dataclass

    • asdict(), astuple(), replace()

  • …and one new class method,

    • fields()

  • frozen=True is now the default!

  • xmod -ed for less cruft

• dataclass.field: Like dataclasses.field, except:

  • default_factory is now a positional parameter

  • perfectly backward compatible

Usage examples

import dataclass
from typing import Dict

@dataclass
class One:
    one: str = 'one'
    two: int = 2
    three: Dict = dataclass.field(dict)  # Simplified `field`

#
# Three new instance methods
#
o = One()
assert o.asdict() == {'one': 'one', 'two': 2, 'three': {}}
assert o.astuple() == ('one', 2, {})

o2 = o.replace(one='seven', three={'nine': 9})
assert o2 == One('seven', 2, {'nine': 9})

#
# A new class method
#
assert [f.name for f in One.fields()] == ['one', 'two', 'three']

#
# Immutable by default
#
try:
    o.one = 'three'
except AttributeError:
    pass
else:
    raise AttributeError('Was mutable!')

@dataclass(frozen=False)
class OneMutable:
    one: str = 'one'
    two: int = 2
    three: Dict = dataclass.field(dict)

om = OneMutable()
om.one = 'three'
assert str(om) == "OneMutable(one='three', two=2, three={})"

#
# These four new methods won't break your old dataclasses:
#
@dataclass
class Overloads:
    one: str = 'one'
    asdict: int = 1
    astuple: int = 1
    fields: int = 1
    replace: int = 1

o = Overloads()
assert ov.one == 'one'
assert ov.asdict == 1
assert ov.astuple == 1
assert ov.fields == 1
assert ov.replace == 1

# In this case, you can access them functions on dataclass:
assert (
    dataclass.asdict(ov) ==
    {'asdict': 1, 'astuple': 1, 'fields': 1, 'one': 'one', 'replace': 1}
)

assert dataclass.astuple(ov) == ('one', 1, 1, 1, 1)