In the following code snippet the dataclass Derived is derived from dataclass Base. The Derived dataclass is setting new default values for field1 and field2.
<code>from dataclasses import dataclass
@dataclass
class Base:
field1: str
field2: str = "default_base_string"
@dataclass
class Derived(Base):
field1 = "default_string1"
field2 = "default_string2"
print(Derived())
</code>
<code>from dataclasses import dataclass
@dataclass
class Base:
field1: str
field2: str = "default_base_string"
@dataclass
class Derived(Base):
field1 = "default_string1"
field2 = "default_string2"
print(Derived())
</code>
from dataclasses import dataclass
@dataclass
class Base:
field1: str
field2: str = "default_base_string"
@dataclass
class Derived(Base):
field1 = "default_string1"
field2 = "default_string2"
print(Derived())
Because Derived is a dataclass and has set a default value for all member variables field1 and field2, I expected that I could simply initialize the class calling Derived(). However I get the following error:
<code>TypeError: Derived.__init__() missing 1 required positional argument: 'field1'
</code>
<code>TypeError: Derived.__init__() missing 1 required positional argument: 'field1'
</code>
TypeError: Derived.__init__() missing 1 required positional argument: 'field1'
Is it not possible to set the default value for a member variable in a derived dataclass, so that this member variable becomes optional in the autogenerated __init__() method? Must I always define my own __init__() method in the Derived class? Or am I doing something wrong here?
To set default values in Derived you need to add the type annotation
<code>@dataclass
class Derived(Base):
field1: str = "default_string1"
field2: str = "default_string2"
print(Derived()) # Derived(field1='default_string1', field2='default_string2')
</code>
<code>@dataclass
class Derived(Base):
field1: str = "default_string1"
field2: str = "default_string2"
print(Derived()) # Derived(field1='default_string1', field2='default_string2')
</code>
@dataclass
class Derived(Base):
field1: str = "default_string1"
field2: str = "default_string2"
print(Derived()) # Derived(field1='default_string1', field2='default_string2')
1