Reference Documentation

Core

mappr.register(src_type, dst_type, strategy=Strategy.CONSTRUCTOR, mapping=None, strict=True)

Register new converter.

Parameters:

Returns:

mappr.convert(dst_type, src_obj, strict=True, strategy=None, **extra)

Convert an object to a given type.

Parameters:

  • dst_type (Type[TypeVar(T)]) – Target type. This is the type of the return value.

  • src_obj – An object to convert. A registered converter will be used to map between the attributes of this object and the target type.

  • strict (bool) – If set to False and the converter is not found for the given type pair, it will create an ad-hoc one that maps the attributes by their name. Defaults to True

Return type:

TypeVar(T)

Returns:

A newly created instance of dst_type with values initialized from src_obj.

Built-in field mappers

mappr.use_default(o)

Indicate we want to use default field value rather than value from source object

Parameters:

  • src_obj – The converted object. Not used here, but part of the mappers interface so has to be defined.

  • name – l Name of the converted field. Not used here, but part of the mappers interface.

Return type:

Any

Returns:

A mapping function for the field. This is just a stub, as mappr.convert will just skip the field if it’s mapper is set to mappr.use_default.

By default, if the attribute exists on the source object, it’s value will be used when creating the result. That happens even if the destination type defines a default value for that field. If you want to use the default provided by the target type you can achive that with mappr.use_default mapper. You simply set the field to mappr.use_default and the attribute value from the source object won’t be used (the target default is used). If the target type does not define a default value an exception will be raised during the creation of the final result.

Example

>>> from dataclasses import dataclass
>>> import mappr
>>>
>>> @dataclass
... class Src:
...     text: str = 'hello'
...     num: int = 10
>>>
>>> @dataclass
... class Dst:
...     text: str
...     num: int = 20
>>>
>>> mappr.register(Src, Dst, mapping=dict(
...     num=mappr.use_default
... ))
>>>
>>> src = Src()
>>> dst = mappr.convert(Dst, src)
>>>
>>> dst.text
'hello'
>>> dst.num
20
mappr.set_const(value)

Always set the field to the given value during conversion.

You can use mappr.set_const if you want to set an attribute to a constant value during conversion, without concern about the source object. Every call to mappr.convert will return the same value.

Parameters:

value (Any) – The value to set on the field. Instead of using the source object attribute or target type field default, this value will be set on the field during conversion.

Return type:

Callable[[TypeVar(T_src), Dict[str, Any]], Any]

Returns:

A mapping function.

Example

>>> from dataclasses import dataclass
>>> import mappr
>>>
>>> @dataclass
... class Src:
...     text: str = 'hello'
...     num: int = 10
>>>
>>> @dataclass
... class Dst:
...     text: str
...     num: int = 20
>>>
>>> mappr.register(Src, Dst, mapping=dict(
...     num=mappr.set_const(100)
... ))
>>>
>>> src = Src()
>>> dst = mappr.convert(Dst, src)
>>>
>>> dst.text
'hello'
>>> dst.num
100