Question

I’m working on a program where the user inputs 3 values (one of which is in dictionary notation form).. but I’m having trouble finding out how to work with this special notation.

The user input will look like this:

{'X':'X+YF','Y':'FX-Y'} 

which I store in a variable p. I know that with p.keys() I get ['X', 'Y'] and with p.values() I get ['X+YF', 'FX-Y'].

How can I relate 'X' to 'X+YF' to say, if the value of the first key in p is 'X', store 'X+YF' in a var, and if the value of the second key in p is 'Y', store 'FX-Y' in a var?

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Is something like this also possible with the same approach stated in the answers below?

 If x is found in some string :
   swap out the X with the value p['X'] 

Answer 1

Are you asking how to get the value associated to a particular key? You can acess a value by putting its key in square brackets:

myDict = {'X':'X+YF','Y':'FX-Y'}
myXVal = myDict['X']
myYVal = myDict['Y']
print myXVal, myYVal

output:

X+YF FX-Y

If you want to have different behavior based on which keys exist in the dict, you can use in:

if 'X' in myDict:
    #do some stuff with myDict['X'] here...

Edit in response to OP’s edit:
My psychic debugging powers tells me that you’re trying to implement an L System. You need to replace all instances of ‘X’ with ‘X+YF’, and all instances of ‘Y’ with ‘FX-Y’. I would implement the function like this:

#path is the string that you want to do replacements in.
#replacementDict is the dict containing the key-value pairs mentioned in your post.
def iterateLSystem(path, replacementDict):
    #strings aren't mutable, so we make a mutable list version of path
    listPath = list(path)
    for i in range(len(listPath)):
        currentChar = listPath[i]
        if currentChar in replacementDict:
            listPath[i] = replacementDict[currentChar]
    #glob listPath back into a single string
    return "".join(listPath)