Pulling variables out of functions in Python

Question

I have been self-teaching Python for a few weeks now and have the aim to create a script to run an equation and keep hitting walls. What I basically want to do is take an input with a unit attached i.e. 6M being 6,000,000, convert the unit into a numerical format and put that into an equation with an output.

So far I have defined a function:

def replaceunit(body):
    body = body.replace(str(body[-1]),str(units.get(body[-1])))
    return body

I have asked for the input and have a dictionary of units (shortened dictionary below):

    T = input("T = ")
    B = input("B = ")

    units ={'M': 1e6,    # mega
            'G': 1e9    # giga
    }

I then try and replace the if an M or G appears in the T or B variables:

    if str(T[-1]).isalpha() == True:
        replaceunit(T)
    if str(B[-1]).isalpha() == True:
        replaceunit(B)

After this I would like the updated T and B to be put into an equation that I define.

If I add a print action to my function I can see the values have been replaced, but have been unable to pull the corrected values through outside of the function and into another equation.

As I say, I'm very new to this, so if there's any help you can lend I'd very much appreciate it. Apologies also if this has been asked elsewhere, the few similar answers I have seen I haven't really understood the answer too.

Can you add code example of a simple "equation"?

Luv
– Luv

2020-05-19 15:29:30 +00:00
Commented May 19, 2020 at 15:29 — Luv
– Luv, Commented May 19, 2020 at 15:29

Luka Mesaric · Accepted Answer · 2020-05-19 15:32:01Z

1

Strings are immutable in Python, meaning they cannot be changed in place, but rather you have to create a new string for every change. That is exactly what you did in replaceunit - you wrote body = body.replace(...) and you replaced the old reference with a new one that replace gave you.

replaceunit is also returning a new reference, so calling it should be done as T = replaceunit(T) and B = replaceunit(B) to save changes. You must not use the same variable if you want to save both the replaced and non-replaced versions of the string.

answered May 19, 2020 at 15:32

Luka Mesaric

6776 silver badges10 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Samwise · Accepted Answer · 2020-05-19 15:33:02Z

If you want the value you returned from replaceunit to be the new value of T, you need to assign it:

T = replaceunit(T)

Note that you could skip the step of assigning body inside the function itself and simply return the value:

def replaceunit(body):
    return body.replace(str(body[-1]),str(units.get(body[-1])))

I would also suggest that it might be more useful to have a function that turns the user-inputted number into an actual number:

def parse_number(body: str) -> float:
    """Converts a string like '2G' into a value like 2000000000."""
    units ={
        'M': 1e6,    # mega
        'G': 1e9,    # giga
    }
    return float(body[:-1]) * units[body[-1]]

This will be necessary if you want to do any actual math with that value!

Collectives™ on Stack Overflow

Pulling variables out of functions in Python

2 Answers 2

Comments

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

Comments

Comments

Your Answer

Sign up or log in

Post as a guest

Related