[21. Preparation and revision of electoral rolls.(1) The electoral roll for each constituency shall be prepared in the prescribed manner by reference to the qualifying date and shall come into force immediately upon its final publication in accordance with the rules made under this Act.
[(2) The said electoral roll
(a) shall, unless otherwise directed by the Election Commission for reasons to be recorded in writing, be revised in the prescribed manner by reference to the qualifying date
(i) before each general election to the House of the People or to the Legislative Assembly of a State; and
(ii) before each bye-election to fill a casual vacancy in a seat allotted to the constituency; and
(b) shall be revised in any year in the prescribed manner by reference to the qualifying date if such revision has been directed by the Election Commission:
Provided that if the electoral roll is not revised as aforesaid, the validity or continued operation of the said electoral roll shall not thereby be affected.]
(3) Notwithstanding anything contained in sub-section (2), the Election Commission may at any time, for reasons to be recorded, direct a special revision of the electoral roll for any constituency or part of a constituency in such manner as it may think fit:
Provided that subject to the other provisions of this Act, the electoral roll for the constituency, as in force at the time of the issue of any such direction, shall continue to be in force until the completion of the special revision so directed.