numpy, for loop exchange_rate

while using the for loop for exchange_rate, im getting the
below error:
exchange_rate = loan_data_strings[:,0]

for i in range(1,13):
    exchange_rate = np.where(exchange_rate = i,
                            EUR_USD[i-1],
                            exchange_rate)

exchange_rate = np.where(exchange_rate = 0,
                         np.mean[EUR_USD],
                         exchange_rate)

SyntaxError: positional argument follows keyword argument