Question about lesson 6 in A Day at the Supermarket


#1

Hello,

I had a question about the following exercise. I completed it already, but I don’t understand why you can archieve the right outcome with just 3 times print. looping trough a dictionary and printing it doesn’t come out in a particular order if I understood correctly in a earlier lesson. So how is it possible that the right price and stock will be printed out under the right kind of fruit and not random. I hope you understand my question since I don’t really know how to explain haha.

prices = {
"banana": 4,
"apple": 2,
"orange": 1.5,
"pear": 3 
}

stock = {
"banana": 6,
"apple": 0,
"orange": 32,
"pear": 15
}

for fruit in prices:
  print fruit
  print "price: %s" % prices[fruit]
  print "stock: %s" % stock[fruit]

Greetings!

Marije


#2

dictionaries consist of key value pairs. Each value is associated with a key. So even though the order of dictionary keys might be “random”, the values associated will the keys stick with the keys

if you have a bunch of people (key) with each a dog on a leash (value), and you would re-arrange there order, each dog owner will keep its own dog (given they have it on a leash). Same with dictionaries, the way dictionaries are implemented in python might mean the keys get shuffled, but each key will keep its associated value


#3

I understand that, but I didn’t define in each print WHICH key I was requesting. If I would have done that, my code would look something like this:

for fruit in prices:
    print "banana"
    print "price: " % prices["banana"]
    print "stock: " % stock["banana"]

etc (for all the kind of fruits)

However I know that is not necessary. But why in my original code isn’t this for example the outcome?:

banana
price: 2
stock: 32

So how does my second and third print know that I requested banana in my first print. So hard to explane what I mean, but I just really want to understand the why and how in my code so I can use it in other scripts in the future.

Thanks!


#4

all of them, using the for .. in loop will request each key and assign it to the iterator (fruit), execute code in the for block, then move on to the next key, until its done with all keys


#5

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