[Tutor] Beginner question (variables, namespaces...)

[Jesse]

Why is it that when one variable is assigned a value in terms of another
variable, assigning a new value to the first doesn't change the value of the
second? This is giving me a huge headache, since I have a bunch of variables
defined in terms of one another, and I want to be able to dynamically update
them (I did not include the definitions of the functions overstock and
roundup, but they work):

stock = float(raw_input("Enter stock (in terms of portions: "))
container = float(raw_input("Enter portions per container: "))
price_per_container = float(raw_input("Enter price per container: "))
weekly_quota = float(raw_input("Enter quota (in terms of portions): "))
extra = overstock(stock, weekly_quota)  # overstock returns 0 if the first
argument is less than the second; otherwise it returns the
                                                              difference
between the first argument and the second.
need = weekly_quota - extra
buy_containers = roundup(need/container) # roundup rounds a non-integer to
the next highest integer
buy_portions = buy_containers * container
leftover = buy_portions - need
cost = price_per_container * buy_containers

I would like to write a function that will update the values of the above
variables given an increase in only the stock variable. Otherwise I'd have
to repeat a bunch of code...:(

Jesse
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