Generating raw_inputs based on user input? [Python]

Question

Is there any way to generate a number of raw_inputs (With unique variables) based on user input? So, say I had this:

if choice == 1:
    noelemen = int(raw_input("Enter total amount of elements: "))

Would there be any way to make it so the integer put in that raw_input field would then "generate" the required amount of raw_inputs? I'd suppose, if it was possible, that it'd make use of functions or something similar, but I'm a bit confused about how I'd get it done to be able to do that.

What I have currently is this:

if noelemen == 1:
        first = raw_input("Enter element: ")

        #Look for the weight of the entered element
        weight1 = float(elemen_data.get(first.lower()))

        if weight1 is not None:
            total_weight = weight1
        print "Total mass =", total_weight

if  noelemen == 2:
        first = raw_input("Enter first element: ")
        second = raw_input("Enter second element: ")

        #Look for the weight of the entered element
        weight1 = float(elemen_data.get(first.lower()))
        weight2 = float(elemen_data.get(second.lower()))

        if weight1 is not None:
            total_weight = weight1 + weight2
        print "Total mass =", total_weight

Which is probably a pretty messy way of doing it, particularly as I'd have to go up to perhaps something like 10 elements, or perhaps even beyond.

So, to repeat... Any way to generate raw_inputs with unique variables based on user input?

Manuzor · Accepted Answer · 2012-08-15 14:01:40Z

4

how about something like this?

elements = []
numberOfPrompts = raw_input("Enter total amount of elements: ")
for i in range(numberOfPrompts):
   # will prompt "Enter Element 1: " on the first iteration
   userInput = raw_input("Enter Element %s" % (i+1, )) 
   elements.append(userInput)

Example case:

>>> Enter total amount of elements: 2 # now hit enter

at this point, the value of the variable numberOfPrompts will be 2. The value of the variable elements will be [], i.e. it is an empty list

>>> Enter Element 1: 3.1415 # hit enter

numberOfPrompts stays 2, elements will be ['3.1415']

>>> Enter Element 2: 2.7182

elements will be ['3.1415', '2.7182']

Now the for-loop is done and you got your user inputs conveniently in the 0-indexed list elements, which you access like a tuple (array):

>>> elements[1]
2.7182

Edit:

After reading your comment I noticed what you intend to do and, just like the other answer stated, it would be best to use a dictionary for this. This should work:

elements = {}
numberOfPrompts = raw_input("Enter total amount of elements: ")
for i in range(numberOfPrompts):
   # will prompt "Enter Element 1: " on the first iteration
   userInput = raw_input("Enter Element %s" % (i+1, )) 
   userInput = userInput.lower()
   elements[userInput] = float(elem_data.get(userInput))

now elements will look like this:

{'oxygen':15.9994, 'hydrogen':1.0079}

you can iterate over all keys like this (to find out, which elements have been entered):

for element in elements.keys():
    print element
# output:
oxygen
hydrogen

To get all values (to sum them up, for instance), do something like this:

weightSum = 0
for weight in elements.values():
    weightSum += weight
print weightSum
# output:
17,0073

Keep in mind that this example is for python 2.x. For python 3.x you will need to adjust a couple of things.

edited Aug 15, 2012 at 14:01

answered Aug 15, 2012 at 12:11

Manuzor

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12 Comments

dantdj Over a year ago

Wait, does this assign a unique variable to each raw_input generated? Currently it just seems to overwrite each previously entered element... Might just be doing something wrong with my lookup, though.

ಠ_ಠ Over a year ago

You will have a list elements, which has numberOfPrompts elements in it, in order.

dantdj Over a year ago

My only problem is that setting it out like this: i.imgur.com/HHYEP.png (Which is the only way that actually prints a value) ends up only giving the weight of the last element entered. The others throw up various errors like AttributeErrors and such.

dantdj Over a year ago

I think we're on different pages, then. I have a CSV file that I'm importing element names and element weights from, so that when you type, for example, Oxygen, it'll search the CSV for it and return 15.9994 (Precise, I know). If you type in Oxygen in one field, then Hydrogen in the next, it'll take those two, look up the weights, then add them together. That kind of thing.

Manuzor Over a year ago

userInput holds an integer. Calling .lower() on it will cause python to throw an error since there is no (built-in) method called .lower() on that object. It worked in your previous code since you were reading the user input directly from the console with raw_input, which returns a string to you. Check out my extended answer to understand how you can get your values.

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Ashwini Chaudhary · Accepted Answer · 2012-08-15 12:09:51Z

1

I would use a dictionary for this:

noelemen = int(raw_input("Enter total amount of elements: "))
elem={}
for x in xrange(1,noelemen+1):
    elem[x]=raw_input("Enter element: ")

answered Aug 15, 2012 at 12:09

Ashwini Chaudhary

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1 Comment

Wooble Over a year ago

IMO, the problem calls out for a list, not a dict with integer keys.

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