Learning rate using "ExponentialLR"

Is it possible to call function to set the value of “gamma” using “ExponentialLR”?

Below code call the function “lambda_rule”

lr.LambdaLR(optimizer, lr_lambda=lambda_rule)

but gives error “TypeError: unsupported operand type(s) for *: ‘float’ and ‘function’” as it is not calling “lambda_rule” function for below code.

lr.ExponentialLR(optimizer, gamma=lambda_rule)