Pure Python sequence query functions using Python 3.12+ generic type syntax

query.py

from typing import (
  Sequence,
  Iterable,
  Callable
)

type Predicate[ T ] = Callable[ [ T ] , bool ]
type Converter[ TIn , TOut ] = Callable[ [ TIn ] , TOut ]

class QueryException( Exception ):
  def __init__( self , *args , **kwargs ):
      super().__init__( *args , **kwargs )

def createmask[ T ]( items : Iterable[ T ] , pred : Predicate[ T ] ) -> Sequence[ bool ]:
  return [ pred( item ) for item in items ]

def applymask[ T ]( items : Sequence[ T ] , mask : Sequence[ bool ] ) -> Sequence[ T | None ]:
  if len( items ) != len( mask ):
    raise QueryException( "length of items not equal to length of mask supplied" )
  return [ item if mask[ i ] else None for i , item in enumerate( items ) ]

def where[ T ]( items : Sequence[ T ] , pred : Predicate[ T ] ) -> Sequence[ T ]:
  new_items : list[ T ] = []
  for item in items: if pred( item ): new_items.append( item )
  return new_items

def select[ TIn , TOut ]( items: Iterable[ TIn ] , converter : Converter[ TIn , TOut ] ) -> Sequence[ TOut ]:
  return [ converter( item ) for item in items ]