Python | Compute the net amount of a bank account based on the transactions

Program:

# computes net bank amount based on the input
# "D" for deposit, "W" for withdrawal 

# define a variable for main amount 
net_amount = 0

while True:
	# input the transaction 
	str = raw_input ("Enter transaction: ")

	# get the value type and amount to the list 
	# seprated by space
	transaction = str.split(" ")

	# get the value of transaction type and amount 
	# in the separated variables
	type = transaction [0]
	amount = int (transaction [1])

	if type=="D" or type=="d":
		net_amount += amount
	elif type=="W" or type=="w":
		net_amount -= amount
	else:
		pass

	#input choice 
	str = raw_input ("want to continue (Y for yes) : ")
	if not (str[0] =="Y" or str[0] =="y") :
		# break the loop 
		break

# print the net amount
print "Net amount: ", net_amount

Output

    Enter transaction: D 10000
    want to continue (Y for yes) : Y
    Enter transaction: W 5000
    want to continue (Y for yes) : Y
    Enter transaction: D 2000
    want to continue (Y for yes) : Y
    Enter transaction: W 100
    want to continue (Y for yes) : N
    Net amount:  6900