Problems using user input between functions
I am trying to learn Python and I am really struggling to keep my code in standalone functions. Here's an example:
def get_inputs():
sales_amount = float(input("Enter total sales amount: "))
def calculate_discount(sales_amount):
discount_amount = sales_amount * 2
return discount_amount
def output():
print ( discount_amount )
def main():
get_inputs()
calculate_discount(sales_amount)
output()
main()
Making this return
File "/Users/Desktop/assA3.py", line 17, in <module>
main()
File "/Users/Desktop/assA3.py", line 14, in main
calculate_discount(sales_amount)
NameError: name 'sales_amount' is not defined
I thought the variable sales_amount
was user-defined before referring to it later. I cannot figure out what I am missing.
I apologize for how basic this problem is, but I'm clearly missing something fundamental and I'm just scared. Any help would be greatly appreciated. Thank.
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You are trying to use function scope variables in other functions. Nothing outside the function get_inputs
can see the variable sales_amount
, its variable is local to that function. You will run into the same problem with discount_amount
which is tied to calculate_discount
.
Instead, return values and pass them to other functions.
def get_inputs():
return float(input("Enter total sales amount: "))
def calculate_discount(sales_amount):
discount_amount = sales_amount * 2
return discount_amount
def output(discount_amount):
print ( discount_amount )
def main():
inputs = get_inputs()
discounts = calculate_discount(inputs)
output(discounts)
main()
A dirty option is to make them global
def get_inputs():
global sales_amount
sales_amount = float(input("Enter total sales amount: "))
def calculate_discount(sales_amount):
global discount_amount
discount_amount = sales_amount * 2
return discount_amount
def output():
print ( discount_amount )
def main():
get_inputs()
calculate_discount(sales_amount)
output()
main()
Globals are slower, make your code harder to maintain, and are bad for a variety of reasons.
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The simple answer is to pass sales_amount
from gets_input()
:
def get_inputs():
sales_amount = float(input("Enter total sales amount: "))
return sales_amount
and use it in main()
:
def main():
sales_amount = get_inputs()
calculate_discount(sales_amount)
output()
If you want to make it "self-contained" you want to use classes:
class Sales(object):
def get_inputs(self):
self.sales_amount = float(input("Enter total sales amount: "))
def calculate_discount(self):
self.discount_amount = self.sales_amount * 2
def output(self):
print ( self.discount_amount )
def main():
my_sale = Sales()
my_sale.get_inputs()
my_sale.calculate_discount()
my_sale.output()
main()
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in each of get_inputs, calculate_discounts and main, sales_amount is a local variable. It might make more sense if each routine uses a different variable name, where all three are currently using sales_amount.
I suggest that get_inputs return a result and main stores the result of get_inputs into a variable, which is then passed to calculate_discounts.
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This is because variables defined in functions are local to Python.
See fooobar.com/questions/1950 / ... to help you understand where you can access variables from.
In your case, you should just pass sales_amount as a parameter to your function as others have pointed out :)
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