Script to obtain a single equation

Question

1.00/5 (1 vote)

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Input in a text file:
a=2*8
b=3*9
c=4*8
d=5*9
e=a+b
f=c+d
g=0*6
h=1*7
i=e+g
j=f+h
output=i+j

Desired Output :
output=(((2*8)+(3*9))*(0*6))+(((4*8)+(5*9))*(1*7))

What I have tried:

Python

#Logic from internet.
D = dict()
output = None
with open('var.txt') as v:
    for line in v:
        k, v = line.strip().split('=')
        if k == 'output':
            output = v
        else:
            D[k] = v
    for k, v in D.items():
        output = output.replace(k, f'({v})')
    print(output)

Posted 14-Nov-21 1:27am

A v Nov2021

Updated 14-Nov-21 2:03am

Richard MacCutchan

v2

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Comments

Richard MacCutchan 14-Nov-21 7:44am

You need to check each entry as you read them and replace the entry with the result of the expression if it contains the keys of existing entries. Thus when you read item e you need to replace "a+b" with the actual values you have already saved earlier.

Patrice T 14-Nov-21 8:02am

What is your question ?

A v Nov2021 14-Nov-21 8:39am

The current script throws a output as (e+g)+(f+h) but i need all elements of e, g, f h too like the desired output i have mentioned. How to modify this script?

Richard MacCutchan 14-Nov-21 8:51am

Se my suggestion above.

A v Nov2021 14-Nov-21 8:59am

I understand the logic, but I don't know how to implement it. I am a naive programmer. The above code snipet is also from the internet.

Richard MacCutchan 14-Nov-21 9:28am

There is no point in copying code from the internet if you do not understand what it is doing. You need to think about how to get the answers you need and write your own code. And if you do it in small steps you can test each step as you go along. The way I would (possibly) do it would be:

for each line of text:
    Split the line at the equals sign into key and expression.
    Using the expression field find out which operator separates the two values. I used a loop like:
        for operator in ['+', '-', '*', '/' ]:
    which allows for the basic four.
    Once you have found the operator, you can split the expression into:
        operand1, operand2, and operator (found in the for loop).
    If either operand has a dictionary entry, then replace it with the dictionary entry's value. Thus 'a' would become '2*8'.
    You then need to recreate the expression from any changed values thus:
        expression = '(' + operand1 + operator + operand2 + ')'

Once you have processed all data then the dictionary entry whose key is 'output' should contain the final expression.

Patrice T 14-Nov-21 9:56am

you need to make your code recursive.

Richard MacCutchan 14-Nov-21 10:56am

My implementation works fine without recursion.

Patrice T 14-Nov-21 12:53pm

By using the word recursive, I want to express the fact that when a variable is replaced by its formula, you need to reapply the same operation to the formula's variables.
I know that 2 nested loops and a boolean will do the trick without resorting to real recursion.

Dave Kreskowiak 14-Nov-21 12:01pm

No you don't. This is a simple dictionary and string replacement app.

Patrice T 14-Nov-21 12:57pm

I said recursive because the replacement operation must reapply to result as long as you find variables.

Dave Kreskowiak 14-Nov-21 13:13pm

Take a look at the input file. There's is a single operation that requires you to go back and reapply anything. All operations chain together in a linear fashion.

Patrice T 14-Nov-21 14:46pm

Agreed, but what if there is another input file ?

Dave Kreskowiak 14-Nov-21 14:47pm

For a school assignment, I doubt it.

A v Nov2021 15-Nov-21 14:41pm

Hi all! Thanks for the inputs, I am just beginning my scripting journey. And yes, it is for a school project.

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