Whenever a power is granted to or duty is imposed upon a public officer or employee the power may be exercised or the duty may be performed by a deputy of such officer or employee or by a person otherwise duly authorized, pursuant to law or ordinance or by an officer of the county of Los Angeles, or by a deputy or employee of such officer when by contract with the city of Temple City such officer is obligated and has agreed to perform certain duties on behalf of the city, unless this code expressly provides otherwise. (1960 Code)