Datatypes

Binmap supports all datatypes that standard library struct has. The types works as typehints in the dataclass. When giving an attribute a typehinted datatype it will be added to the binary output from the class.

Padding

Padding is a field type and datatype that is length bytes long, and will not show up as attributes in the dataclass. Trying to assign it a value will be silently ignored and reading from will raise the AttributeException exception.

>>> class PaddedData(BinmapDataclass):
...     temp: signedchar = 0
...     pad1: pad = padding(length = 5)
...
>>> pd = PaddedData()
>>> pd.temp = 14
>>> print(bytes(pd))
b'\x0e\x00\x00\x00\x00\x00'

Constant

Constant is fieldtype that always is the given value. Constant could be of any datatype.

>>> class Constant(BinmapDataclass):
...     signature: unsignedshort = constant(0x1313)
...     temp: unsignedchar = 0
...
>>> c = Constant()
>>> c.temp = 18
>>> print(bytes(c))
b'\x13\x13\x12'

>>> print(c.signature)
4883
>>> print(c.temp)
18

>>> c.signature = 10
AttributeError: signature is a constant

Enums

Enumfield maps agaings IntEnum or IntFlag so that you could set the value either as the enum or as the numeric value.

>>> class WindEnum(IntEnum):
...     North = 0
...     East = 1
...     South = 2
...     West = 3
...
>>> class Wind(BinmapDataclass):
...     speed: unsignedchar = 0
...     direction: unsignedchar = enumfield(WindEnum, default=WindEnum.East)
...
>>> w = Wind()
>>> print(w)
Wind(speed=0, direction=<WindEnum.East: 1>)
>>> w.direction = WindEnum.West
>>> print(w.direction)
<WindEnum.West: 3>
>>> w.direction = 2
>>> print(w.direction)
<WindEnum.South: 2>

Autolength

Autolenght field types counts number of bytes in the output, including the autolength field it self. You can’t set an autolenght field. Autolength can be offseted, for example to ignore it’s own length.

>>> class MyBinStruct(BinmapDataclass):
...     length: unsignedchar = autolength()
...     temp: signedchar = 0
...
>>> mb = MyBinStruct()
>>> print(mb)
MyBinStruct(length=2, temp=0)
>>> mb.length = 10
AttributeError: length is a constant

Calculated fields

Calculated fields calls a function when data is converted to binary value. The function must be declared when the field is added.

>>> class WithChecksum(BinmapDataclass):
...     temp: signedchar = 0
...     hum: unsignedchar = 0
...     def chk(self) -> unsignedchar:
...         return (self.temp + self.hum) & 0xFF
...     checksum: unsignedchar = calculatedfield(chk)
...
>>> wc = WithChecksum()
>>> wc.temp = -20
>>> wc.hum = 10
>>> print(wc)
WithChecksum(temp=-20, hum=10, checksum=246)
>>> print(bytes(wc))
b'\xec\n\xf6'