CODEWITHSUNDEEP
python
ToCa81
ToCa81

Reputation: 37

How do you append a list in a while loop without overwriting previous results

I'm writing a script for a grocery list for my course on Python. Everything looks good, except every time I append my list with a new dictionary entry, I overwrite the old values. I found a lot of similar questions on here already, but I hate to admit that I didn't quite understand a lot of the answers yet. Hopefully I can understand it a little better if I ask the question myself and know the context. Here is my code:

grocery_item = {}
grocery_history = []
stop = 'c'
while stop == 'c':
  item_name = input('Item name:\n')    
  quantity = input('Quantity purchased:\n')  
  cost = input('Price per item:\n')
  grocery_item = {'name':item_name, 'number': int(quantity), 'price': 
  float(cost)}
  grocery_history.append(grocery_item)   <<< # OVERWRITES OLD VALUES.
  stop = input("Would you like to enter another item?\nType 'c' for 
  continue 
  or 'q' to quit:\n")
grand_total = 0
for items in range(0,len(grocery_history)): 
  item_total = grocery_item['number'] * grocery_item['price']
  grand_total = grand_total + item_total
  print(str(grocery_item['number']) + ' ' + str(grocery_item['name']) + ' 
  ' + '@' + ' ' + '$' + str(grocery_item['price']) + ' ' + 'ea' + ' ' + 
  '$' + 
  str(item_total))
  item_total == 0
print('Grand total:$' + str(grand_total))

So instead of each input being saved and totaled up, it just overwrites all the previous inputs with the value of the last input entered and adds that up however many times it iterated through the loop. I understand why it overwrites the previous values and it makes perfect sense. I just don't know how to update the list while still outputting the original inputs. Thanks in advance for any help!

Upvotes: 2

Views: 1376

Answers (2)

glhr
glhr

Reputation: 4537

The problem isn't where you think it is. The values are being appended correctly to grocery_history. You can check that yourself with print(grocery_history).

The problem is in your for loop. You're reading from grocery_item (ie. the last item entered by the user) instead of from the whole grocery_history list. Replace your for loop with this one:

for i in range(0,len(grocery_history)):
  item_total = grocery_history[i]['number'] * grocery_history[i]['price']
  grand_total = grand_total + item_total
  print(str(grocery_history[i]['number']) + ' ' + str(grocery_history[i]['number']) + ' ' + '@' + ' ' + '$' + str(grocery_history[i]['number']) + ' ' + 'ea' + ' ' + '$' + str(item_total))
  item_total == 0
print('Grand total:$' + str(grand_total))

Upvotes: 0

Davis Herring
Davis Herring

Reputation: 39788

You create several dict objects and assign each to grocery_item. Each replaces the last under that name, which is fine because you also append each to grocery_history. However, you never use that list (except to determine how many iterations of the totaling loop to perform); instead, you use grocery_item again, which still has whatever single value you assigned to it last.

Just replace

for items in range(0,len(grocery_history)):

with

for grocery_item in grocery_history:

(You weren’t ever using items anyway.)

Upvotes: 3

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