将变量名传递给函数？

Question

I have a function that contains several variables, but I only want to run it for one variable at the time. For example only for "exrate". The idea is to pass "exrate" into the function and then for-loop "exrate" only and calculate the result. Unfortunately the the value "turnover" does not change.

exrate = 100
sales = 0

def sim(var, min, max):
    for var in range(min, max):
        turnover = 1000 * (exrate/100) + sales
        print(turnover)

sim(exrate, 100, 105)
sim(sales, 1000, 1100)

Answer 1

Let's try to refactor your original code a bit:

exrate = 100
sales = 0

def sim(var, min, max):
    for var in range(min, max):
        turnover = 1000 * (exrate/100) + sales
        print(turnover)

First, we can factor out the function used in sim, which would be:

def f(exrate, sales):
    return 1000 * (exrate/100) + sales

and that function can be simplified further 1000/100=10 :

def f(exrate, sales):
    return 10 * exrate + sales

You're using globals exrate=100, sales=0 but that's not a good idea, so lets' get rid of those globals by just using default parameters:

def f(exrate=100, sales=0):
    return 10 * exrate + sales

Now, at this point we've got a mathy function we can use as input to another functions, it's a function with one single responsability.

So let's say we want to see how this function evolves with respect to one of its independent variables (exrate or sales) :

for i in range(100, 1000, 100):
    print(f(exrate=i))

for i in range(0, 1000, 200):
    print(f(sales=i))

Or both:

for i in range(0, 1000, 200):
    print(f(exrate=200, sales=i))

The main idea would be, when simulating something is a good idea to split the code into code that does the simulation (plotting the function in a graph, print values onto a console, ...) and the code which is the simulation itself (in this case, a simple linear function of the form f(x)=ax+b )

Answer 2

You are using a variable external to the function in the definition. Consider replacing exrate with var within the function definition.