CODEWITHSUNDEEP
pythonpython-3.x
mmghu
mmghu

Reputation: 621

Python's if key in dictionary not working correctly

I'm working on a programming problem where user input can define variables, like so:

length = 1

When the user does this, I store the pair in a dictionary:

{'length': '1'}

The problem is, when I later try to check if a key exists in the dictionary, I always get False, even if it is definitely in there. Here is my code:

import math

def main():
    curr_formula = input()
    substitutions = dict()

    while(curr_formula != "0"):
        if("=" in curr_formula):
            split_formula = curr_formula.split("=")
            substitutions[split_formula[0]] = split_formula[1]

        curr_split = curr_formula.split(" ")
        for i in range(len(curr_split)):

            # this if statement never runs for some reason
            if(curr_split[i] in substitutions):
                curr_split[i] = substitutions[curr_split[i]]

        print(''.join(curr_split))

        curr_formula = input()
main()

The input "length = 1" and then "length + 2" should print "1 + 2" but instead cannot detect that the key already exists. Any insight on this issue would be much appreciated!

Upvotes: 0

Views: 1421

Answers (1)

Peter Gibson
Peter Gibson

Reputation: 19554

When you split on '=', there is a space after the first term and before the second.

>>> 'length = 1'.split('=')
['length ', ' 1']

Whereas when you split on ' ' it's removed.

>>> 'length = 1'.split(' ')
['length', '=', '1']

As a result, the keys in your dict are probably different.

Upvotes: 2

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