Python Question: How to add the values per line - python-3.x

Question

I'm new in Python and trying to get my head around on this code.
We have to import a text file named line-items.txt; excerpt of the txt are as follows including its heading:
product name quantity unit price
product a 1 10.00
product b 5 19.70
product a 3 10.00
product b 7 19.70
We need to write a code that will search for the product name and sum its quantity and unit price then the sales revenue formula would be "total unit price of the product" * "total quantity of the product"; we have to create new text file and the output should be something like this:
product name sales volume sales revenue
product a 4 40.0
product b 12 236.39999999999998
On my code below it has searched the quantity of product b which is 5 and 7 and its unit price (I did print statement to check its output but on the code below I commented the unit price for simplicity) but it's not adding the values that it has searched:
def main():
# opening file to read line-items.txt
with open("line-items.txt", "r") as line_items:
# to get the list of lines and reading the second line of the text
prod_b = 0
newtxt = line_items.readlines()[1:]
for line in newtxt:
text = line.strip().split()
product_name = text[0:2]
quantity = text[2]
unit_price = text[3]
if product_name == ['product', 'b']:
prod_b += int(quantity)
unit_price_b = float(unit_price)
# print(unit_price_b)
print(quantity)
line_items.close()
if name == 'main':
main()
The output of the code above are as follows; it's not adding 5 and 7; what am I doing wrong?
5
7
Thanks,
Rogue

Answer 1

While the answer provided by #JonSG is certainly more elegant. The problem with your code is quite simple and is caused by an indentation error. You need to indent the if statement under the for loop as shown below:
def main():
# opening file to read line-items.txt
with open("line-items.txt", "r") as line_items:
# to get the list of lines and reading the second line of the text
prod_b = 0
newtxt = line_items.readlines()[1:]
for line in newtxt:
text = line.strip().split()
product_name = text[0:2]
quantity = text[2]
unit_price = text[3]
if product_name == ['product', 'b']:
prod_b += int(quantity)
unit_price_b = float(unit_price)
# print(unit_price_b)
print(quantity)
line_items.close()

Answer 2

Using a nested collections.defaultdict makes this problem rather straightforward.
import collections
import json
results = collections.defaultdict(lambda: collections.defaultdict(float))
with open("line-items.txt", "r") as line_items:
next(line_items) ## skip first line
for row in line_items.readlines():
cells = row.split(" ")
product_name = f"{cells[0]} {cells[1]}"
quatity = int(cells[2])
price = float(cells[3])
results[product_name]["quantity"] += quatity
results[product_name]["sales volume"] += quatity * price
print(json.dumps(results, indent=4))
results in:
{
"product a": {
"quantity": 4.0,
"sales volume": 40.0
},
"product b": {
"quantity": 12.0,
"sales volume": 236.4
}
}