How many episodes were written by Warren Leight?
CREATE TABLE "table1_29154676_1" (
  "season_no" real,
  "series_no" real,
  "title" text,
  "directed_by" text,
  "written_by" text,
  "original_air_date" text,
  "production_code" real,
  "u_s_viewers_millions" text
);
SELECT COUNT("season_no") FROM "table1_29154676_1" WHERE "written_by"='Warren Leight';