python solve equation inside string

Question

I have this code

ecuation=("95502+45806-85773-659740")
answer = sum(int(x) for x in ecuation if x.isdigit())
print(answer)

Which prints this as answer

This is not correct, the idea is to get the ecuation from a web page (I already have that part working) and solve it.

note: The ecuation will always change but it will always be adding and substracting numbers.

how about `eval()` Be careful though if the equations are from user input this could be a security issue, because harmful code could get run this way... — Heiner Früh, Jun 07 '19 at 15:43

score 3 · Answer 1 · answered Jun 07 '19 at 15:42

3

You can try using the eval function:

>>> ecuation=("95502+45806-85773-659740")
>>> eval(ecuation)
-604205

However, you need to be very careful while using this. A safer way is:

>>> import ast
>>> ast.literal_eval(ecuation)
-604205

answered Jun 07 '19 at 15:42

rassar

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Good idea to advise using literal_eval – Bertrand Gazanion Jun 07 '19 at 15:43
literal_eval only works with additions. Not with multiplications or divisions. But good trick. – Jean-François Fabre Jun 07 '19 at 15:51

score 0 · Answer 2 · answered Jun 07 '19 at 15:42

0

Try

ecuation=("95502+45806-85773-659740")
answer = eval(ecuation)
print(answer)

answered Jun 07 '19 at 15:42

Vitor Falcão

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score 0 · Answer 3 · answered Jun 07 '19 at 15:44

0

Using re:

import re

ecuation= "95502+45806-85773-659740"

s = sum(int(g) for g in re.findall(r'((?:\+|-)?\d+)', ecuation))
print(s)

Prints:

-604205

answered Jun 07 '19 at 15:44

Andrej Kesely

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Not sure if this is important, but this will not work for decimals. – rassar Jun 07 '19 at 15:45

score 0 · Accepted Answer · answered Jun 07 '19 at 15:44

What you're doing is this calculation:

9+5+5+0+2+4+5+8+0+6+8+5+7+7+3+6+5+9+7+4+0=105

What you want to do is break apart the string and add/subtract those numbers. This can be shortcut by using eval() (more here), as suggested by Vitor, or with ast.literal_eval (more here), as suggested by rassar.

python solve equation inside string

4 Answers4