Moving the _get method length checks into the dtype method.

bitstring/bits.py

@@ -780,14 +780,10 @@ def _getintle(self) -> int:
         return bs.slice_to_int()
 
     def _gete4m3float(self) -> float:
-        if len(self) != 8:
-            raise InterpretError(f"A e4m3float must be 8 bits long, not {len(self)} bits.")
         u = self._getuint()
         return e4m3float_fmt.lut_int8_to_float[u]
 
     def _gete5m2float(self) -> float:
-        if len(self) != 8:
-            raise InterpretError(f"A e5m2float must be 8 bits long, not {len(self)} bits.")
         u = self._getuint()
         return e5m2float_fmt.lut_int8_to_float[u]
 
@@ -800,10 +796,7 @@ def _setfloatbe(self, f: float, length: Optional[int] = None, _offset: None = No
 
     def _getfloatbe(self) -> float:
         """Interpret the whole bitstring as a big-endian float."""
-        try:
-            fmt = {16: '>e', 32: '>f', 64: '>d'}[len(self)]
-        except KeyError:
-            raise InterpretError(f"Floats can only be 16, 32 or 64 bits long, not {len(self)} bits")
+        fmt = {16: '>e', 32: '>f', 64: '>d'}[len(self)]
         return struct.unpack(fmt, self._bitstore.tobytes())[0]
 
     def _setfloatle(self, f: float, length: Optional[int] = None, _offset: None = None) -> None:
@@ -815,15 +808,10 @@ def _setfloatle(self, f: float, length: Optional[int] = None, _offset: None = No
 
     def _getfloatle(self) -> float:
         """Interpret the whole bitstring as a little-endian float."""
-        try:
-            fmt = {16: '<e', 32: '<f', 64: '<d'}[len(self)]
-        except KeyError:
-            raise InterpretError(f"Floats can only be 16, 32 or 64 bits long, not {len(self)} bits")
+        fmt = {16: '<e', 32: '<f', 64: '<d'}[len(self)]
         return struct.unpack(fmt, self._bitstore.tobytes())[0]
 
     def _getbfloatbe(self) -> float:
-        if len(self) != 16:
-            raise InterpretError(f"bfloats must be length 16, received a length of {len(self)} bits.")
         zero_padded = self + Bits(16)
         return zero_padded._getfloatbe()
 
@@ -833,8 +821,6 @@ def _setbfloatbe(self, f: Union[float, str], length: Optional[int] = None, _offs
         self._bitstore = bfloat2bitstore(f)
 
     def _getbfloatle(self) -> float:
-        if len(self) != 16:
-            raise InterpretError(f"bfloats must be length 16, received a length of {len(self)} bits.")
         zero_padded = Bits(16) + self
         return zero_padded._getfloatle()
 
@@ -983,8 +969,6 @@ def _setbool(self, value: Union[bool, str], length: Optional[int] = None, _offse
             raise CreationError(f"Cannot initialise boolean with {value}.")
 
     def _getbool(self) -> bool:
-        if len(self) != 1:
-            raise InterpretError(f"For a bool interpretation a bitstring must be 1 bit long, not {len(self)} bits.")
         return self[0]
 
     def _getpad(self) -> None:

bitstring/dtypes.py

@@ -98,7 +98,21 @@ def __init__(self, name: str, set_fn, get_fn, return_type: Any = Any, is_signed:
         self.multiplier = multiplier
 
         self.set_fn = set_fn
-        self.get_fn = get_fn    # Interpret everything
+
+        if self.fixed_length:
+            if len(self.fixed_length) == 1:
+                def length_checked_get_fn(bs):
+                    if len(bs) != self.fixed_length[0]:
+                        raise InterpretError(f"'{self.name}' dtypes must have a length of {self.fixed_length[0]}, but received a length of {len(bs)}.")
+                    return get_fn(bs)
+            else:
+                def length_checked_get_fn(bs):
+                    if len(bs) not in self.fixed_length:
+                        raise InterpretError(f"'{self.name}' dtypes must have one of the lengths {self.fixed_length}, but received a length of {len(bs)}.")
+                    return get_fn(bs)
+            self.get_fn = length_checked_get_fn  # Interpret everything and check the length
+        else:
+            self.get_fn = get_fn  # Interpret everything
 
         # Create a reading function from the get_fn.
         if self.is_unknown_length:
@@ -121,7 +135,6 @@ def read_fn(bs, start):
                 def read_fn(bs, start, length):
                     return self.get_fn(bs[start:start + length])
             self.read_fn = read_fn
-
         self.bitlength2chars_fn = bitlength2chars_fn
 
     def getDtype(self, length: Optional[int] = None) -> Dtype: