Why does naming a dataclass field `date` cause RecursionError?

Question

from datetime import date import dataclasses @dataclasses.dataclass(frozen=True) class A: date: date = dataclasses.field() Traceback (most recent call last): File "", line 1, in File "/usr/local/Cellar/python/3.7.7/Frameworks/Python.framework/Versions/3.7/lib/python3.7/dataclasses.py", line 1002, in wrap return _process_class(cls, init, repr, eq, order, unsafe_hash, frozen) File "/usr/local/Cellar/python/3.7.7/Frameworks/Python.framework/Versions/3.7/lib/python3.7/dataclasses.py", line 979, in _process_class str(inspect.signature(cls)).replace(' -> None', '')) File "/usr/local/Cellar/python/3.7.7/Frameworks/Python.framework/Versions/3.7/lib/python3.7/inspect.py", line 3040, in __str__ formatted = str(param) File "/usr/local/Cellar/python/3.7.7/Frameworks/Python.framework/Versions/3.7/lib/python3.7/inspect.py", line 2558, in __str__ formatannotation(self._annotation)) File "/usr/local/Cellar/python/3.7.7/Frameworks/Python.framework/Versions/3.7/lib/python3.7/inspect.py", line 1199, in formatannotation return repr(annotation) File "/usr/local/Cellar/python/3.7.7/Frameworks/Python.framework/Versions/3.7/lib/python3.7/dataclasses.py", line 249, in __repr__ return ('Field(' File "/usr/local/Cellar/python/3.7.7/Frameworks/Python.framework/Versions/3.7/lib/python3.7/dataclasses.py", line 249, in __repr__ return ('Field(' File "/usr/local/Cellar/python/3.7.7/Frameworks/Python.framework/Versions/3.7/lib/python3.7/dataclasses.py", line 249, in __repr__ return ('Field(' [Previous line repeated 491 more times] RecursionError: maximum recursion depth exceeded But this works: @dataclasses.dataclass(frozen=True) class A: date: date So does this: @dataclasses.dataclass(frozen=True) class A: date_: date = dataclasses.field() Is that a bug, or by design? Select the correct answer from above options

Answer 1

This: date: date = dataclasses.field() doesn't annotate date as datetime.date. It annotates date as dataclasses.field(), because annotation is evaluated after assignment. dataclasses doesn't expect the field to have itself as its annotation, and you didn't want that either. Use something like import datetime import dataclasses @dataclasses.dataclass(frozen=True) class A: date: datetime.date = dataclasses.field() If you want to know more about the Data Science then do check out the following Data Science which will help you in understanding Data Science from scratch