<?php echo "hello world"; ?> explain line by line and give me similar code like this in python

def gain_or_loss_calculator(mutual_fund_A, mutual_fund_B):
    gain_or_loss = ((mutual_fund_A - mutual_fund_B)/mutual_fund_B)
    return gain_or_loss

mutual_fund_A = 1000
mutual_fund_B = 1100
print(gain_or_loss_calculator(mutual_fund_A, mutual_fund_B))