45c2da35-8699-4cad-a3c8-087dff6fb978
commented
4 years ago After instantiation of a variable of a DataClass, it is possible to assign new attributes (that were not defined in defining the DataClass):
data.new_attribute = 3.0 # does NOT raise Error!This gives unexpected behaviour: if you print the variable, then 'new_attribute' is not printed (since it is not in the definition of the DataClass).
Assigning to an attribute is therefore not typo-safe (which users may expect from a DataClass).
I would expect the behaviour of the DataClass be consistent and typo-safe.
Attached is a file that demonstrates the bug (behaviour) and provides a 'SafeDataClass' by overriding the __setattr__ method.
My suggestion would be to the adjust the library __setattr__ for the DataClass such that is will be typo-safe.
Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.
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GitHub fields: ```python assignee = None closed_at = None created_at =
labels = ['3.7', '3.8', 'type-bug', 'library', '3.9']
title = 'DataClass typo-unsafe attribute creation & unexpected behaviour (dataclasses)'
updated_at =
user = 'https://bugs.python.org/marcelpvisser'
```
bugs.python.org fields:
```python
activity =
actor = 'xtreak'
assignee = 'none'
closed = False
closed_date = None
closer = None
components = ['Library (Lib)']
creation =
creator = 'marcelpvisser'
dependencies = []
files = ['48865', '48866']
hgrepos = []
issue_num = 39462
keywords = []
message_count = 2.0
messages = ['360752', '360753']
nosy_count = 2.0
nosy_names = ['eric.smith', 'marcelpvisser']
pr_nums = []
priority = 'normal'
resolution = None
stage = None
status = 'open'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue39462'
versions = ['Python 3.7', 'Python 3.8', 'Python 3.9']
```