data: add Pad type

sx/__init__.py

@@ -5,7 +5,7 @@ from .core.expr import BaseExpr, Expr, const, infer, bool_, not_, and_, or_, in_
 from .core.meta import Wrapper, Generic
 del core
 
-from .types.data import Nothing, Static, Ignored, Data, data, Bits, bit, nibble
+from .types.data import Nothing, Static, Ignored, Pad, Data, data, Bits, bit, nibble
 from .types.num import (
     Bool, Int, Float, bool, int8, uint8, byte,
     int16, uint16, int16be, int16le, uint16be, uint16le, word,

sx/types/data.py

@@ -27,7 +27,36 @@ class Nothing(Type[None]):
     def __repr__(self) -> str:
         return '{__name__}.Nothing()'
 
+class Pad(Type[None]):
+    """ Seek something, yield nothing. """
+    __slots__ = ('amount', 'value')
+
+    def __init__(self, amount=0, value=b'\x00'):
+        self.amount = amount
+        self.value = value
+
+    def parse(self, context: Context, stream: Stream) -> None:
+        stream.seek(context.get(self.amount), os.SEEK_CUR)
+
+    def dump(self, context: Context, stream: Stream, value: None) -> None:
+        value = stretch(context.get(self.value), context.get(self.amount))
+        stream.write(value)
+
+    def sizeof(self, context: Context) -> O[Pos]:
+        return context.peek(self.amount)
+
+    def default(self, context: Context) -> None:
+        return None
+
+    def __str__(self) -> str:
+        return f'[padding: {self.amount}]'
+
+    def __repr__(self) -> str:
+        return f'{__name__}.Pad({self.amount!r}, value={self.value!r})'
+
+
 class Data(Type[bytes]):
+    """ Parse/dump and yield bytes. """
     __slots__ = ('size',)
 
     def __init__(self, size: U[D, O[int]] = None) -> None:
@@ -62,8 +91,8 @@ class Data(Type[bytes]):
 
 data = Data()
 
-
 class Bits(Type[int]):
+    """ Parse/dump and yield bits. """
     __slots__ = ('amount',)
 
     def __init__(self, amount: U[D, int] = 0) -> None: