ValueError: mutable default <class 'flet.alignment.Alignment'> for field begin is not allowed: use default_factory

[LeMeteore]

Context:

• Ubuntu 21.10
• flet 0.1.48
• Python 3.11.0b4

I was trying to follow the introduction and I received this traceback:

>> python3 app.py 
Traceback (most recent call last):
  File "/home/nsukami/GIT/flet_example/app.py", line 1, in <module>
    import flet
  File "/home/nsukami/vrtlnvs/flet/lib/python3.11/site-packages/flet/__init__.py", line 11, in <module>
    from flet.container import Container
  File "/home/nsukami/vrtlnvs/flet/lib/python3.11/site-packages/flet/container.py", line 9, in <module>
    from flet.gradients import Gradient
  File "/home/nsukami/vrtlnvs/flet/lib/python3.11/site-packages/flet/gradients.py", line 25, in <module>
    @dataclasses.dataclass
     ^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dataclasses.py", line 1221, in dataclass
    return wrap(cls)
           ^^^^^^^^^
  File "/usr/local/lib/python3.11/dataclasses.py", line 1211, in wrap
    return _process_class(cls, init, repr, eq, order, unsafe_hash,
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dataclasses.py", line 959, in _process_class
    cls_fields.append(_get_field(cls, name, type, kw_only))
                      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.11/dataclasses.py", line 816, in _get_field
    raise ValueError(f'mutable default {type(f.default)} for field '
ValueError: mutable default <class 'flet.alignment.Alignment'> for field begin is not allowed: use default_factory
(flet) ~/GIT/flet_example 

Is there something I'm doing correctly ?

The only Python class with an attribute named begin is here. If there is really a bug somewhere, is there anything I can do to help you fix this ?

o/

[FeodorFitsner]

Thanks for reporting that!

Could you please try replacing begin: Alignment = field(default=alignment.center_left) with begin: Alignment = field(default_factory=alignment.center_left) in "/home/nsukami/vrtlnvs/flet/lib/python3.11/site-packages/flet/gradients.py", line 27 to see if that fixes that error?

[FeodorFitsner]

This explains an issue more:
https://stackoverflow.com/a/52064202
https://stackoverflow.com/a/53633297

I'm not sure why it's not reproducible with Python 3.10, but definitely it looks like a bug.

[LeMeteore]

Could you please try replacing [...] to see if that fixes that error?

I've made the following modifications inside /home/nsukami/vrtlnvs/flet/lib/python3.11/site-packages/flet/gradients.py and the error was fixed:

@dataclasses.dataclass
class LinearGradient(Gradient):
    # begin: Alignment = field(default=alignment.center_left)
    begin: Alignment = field(default_factory=alignment.center_left)
    # end: Alignment = field(default=alignment.center_right)
    end: Alignment = field(default_factory=alignment.center_right)
    type: str = field(default="linear")


@dataclasses.dataclass
class RadialGradient(Gradient):
    # center: Alignment = field(default=alignment.center)
    center: Alignment = field(default_factory=alignment.center)
    radius: Union[float, int] = field(default=0.5)
    focal: Alignment = field(default=None)
    focal_radius: Union[float, int] = field(default=0.0)
    type: str = field(default="radial")


@dataclasses.dataclass
class SweepGradient(Gradient):
    # center: Alignment = field(default=alignment.center)
    center: Alignment = field(default_factory=alignment.center)
    start_angle: Union[float, int] = field(default=0.0)
    end_angle: Union[float, int] = field(default=math.pi * 2)
    type: str = field(default="sweep")

[FeodorFitsner]

So, it's been fixed in https://pypi.org/project/flet/0.1.49/ - please update flet module and give it another try.