How can I divide all of the data in the second row by two?
recipe = [
['eggs', 'flour', 'meat'],
[4, 250, 5],
['large','grams', 'kg'],
]
I've tried starting with
for row[2] in recipe:
But I get an error saying:
Traceback (most recent call last):
File "/Users/g/Documents/reicpe.py", line 7, in for row[2] in meat_pie:
NameError: name 'row' is not defined
You can also use list comprehension and do it in one single line without the for-loop:
recipe[1] = [num / 2 for num in recipe[1]]
Code Explanation [num / 2 for num in recipe[1]]:
recipe[1]: This is a list, it's the second element of recipe list
The second element of recipe is: [4, 250, 5]
for num in recipe[1]: This mean that we're going to loop over the elements of recipe[1], so num it's a variable, and it's value changes over the list elements in each iteration.
num / 2: It's obvious that we get num and divide by 2
recipe = [
['eggs', 'flour', 'meat'],
[4, 250, 5],
['large','grams', 'kg'],
]
Leaving aside this would be far better as a dictionary, if you want to divide the quantities by two, and change what you have stored :
for quantity, index in enumerate(recipe[1])
recipe[1][index] = quantity/2
A better way would be to use a dictionary, which allows you to give names to data items :
recipe = {"eggs":{"quantity":4, "measurement":"large"},
"flour":{"quantity":250,"measurement":"grams"},
"meat":{"quantity":5,"measurement":"kg"}}
and now division by two becomes :
for ingredient in recipe:
recipe[ingredient]["quantity"] = recipe[ingredient]["quantity"]/2
and print the recipe becomes :
for ingredient in recipe:
print "{} {} {}".format(recipe[ingredient]["quantity"], recipe[ingredient]["measurement"], ingredient)
this generates :
4 large eggs
250 grams flour
5 kg meat
and no faffing about with index numbers etc.
recipe[1] gives you the second list inside the recipe list. Remember, list index always start with 0.
Then:
for row in recipe[1]:
Will iterate with row taking the value of each of the values inside recipe[1].
You're trying to iterate on the wrong portion. When you use the statement: for i in list, i is created as a new variable (as if you had just stated i = 5). So at that point, it does not have a getter (index or otherwise) for element 5 (and it is not a valid variable name).
To fix your iteration issue try:
for row in mylist[index]:
That will iterate over the list at index in mylist, of course remember that lists are 0 indexed (your numbers are at index 1).
You're going to have another issue shortly with updating the values in your array, however, since the process will create a copy the way you're doing it. A simple fix is to use enumerate (but I will leave that up to you to try out before giving it to you!)
