CODEWITHSUNDEEP
pythonpython-2.7
wes1099
wes1099

Reputation: 98

Having user input variables to be used in a later equation

I am writing a program to calculate the mass of a given molecule. I have defined every element as an integer. I need to be able to type in a chemical formula like NaCl and have it print out the sum of the atomic masses of Na and Cl. So far I have things set up so that I can type in a chemical formula and it turns it into a list of elements, so if I typed in NaCl it would give me ['Na', 'Cl']. Here is the code:

import re
Na = 22.99
Cl = 35.45
input = raw_input()
inputList = (re.findall('[A-Z][^A-Z]*', input))

Firstly I need to know how to tell the computer I am inputting variables that I previously defined, not strings. Then I want to make it assign each item from the list to its own variable. Something like

e1 = Na
e2 = Cl

My main issue is that at the moment my input is treated as a string.

Upvotes: 1

Views: 91

Answers (3)

TigerhawkT3
TigerhawkT3

Reputation: 49330

Use the sum() and map() functions to add up the appropriate values from a dictionary:

>>> elements = {'Na':22.99, 'Cl':35.45}
>>> result = ['Na', 'Cl']
>>> answer = sum(map(elements.get, result))
>>> answer
58.44

Upvotes: 2

David Zemens
David Zemens

Reputation: 53663

Using a dictionary, you can easily take string input and handle it:

elements = { 'Na': 22.99,
             'Cl': 35.45
           }  # You can extend this dictionary to include more elements

print elements.get(raw_input('Enter an element symbol:   ', 'invalid'))  
"""
use the .get method to return a placeholder value, 
representing that the *input* value doesn't exist in the dictionar
"""

Upvotes: 1

Prune
Prune

Reputation: 77910

I believe what you want is a dictionary, like so:

atomic_wt = {'Na':22.99, 'Cl':35.45}

Later, when you have your inputs, you can access them in a loop:

for element in inputList:
    elem_wt = atomic_wt[element]

Upvotes: 2

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