.BZ2File: ClassType
.BZ2File.
    # TODO: should be a procedure
    __call__: (filename: Str, mode := Str) -> .BZ2File
    peek: (self: Ref(.BZ2File), n := Nat) -> Str
    read!: (self: RefMut(.BZ2File), size := Nat or {-1}) => Str
    readline!: (self: RefMut(.BZ2File), size := Nat or {-1}) => Str
    close!: (self: RefMut(.BZ2File)) => NoneType
    closed: (self: Ref(.BZ2File)) -> Bool
    write!: (self: RefMut(.BZ2File), data: Str) => Nat
    flush!: (self: RefMut(.BZ2File)) => NoneType
    seek!: (self: RefMut(.BZ2File), offset: Nat, whence := Nat) => Nat

.open!: (filename: Str, mode := Str, compresslevel := Nat, encoding := Str) => .BZ2File