CODEWITHSUNDEEP
pythonvariableswhile-loop
Ollie
Ollie

Reputation: 117

Setting new variables in a while loop with calculations PYTHON

I'm running a population model, and the wrong numbers always come out because I'm setting the variables to new values, but then when I want to use the old variables, the loop automatically updates itself and uses the new ones.

juvenile_population = 10
adult_population = 10
senile_population = 1
juvenile_survival = 1
adult_survival = 1
senile_survival = 0
birth_rate = 2
generations = 5


counter = 0
while counter < generations:
    juvenile_population = adult_population * birth_rate
    adult_population = juvenile_population * juvenile_survival
    senile_population = (adult_population * adult_survival) (senile_population * senile_survival)
    total_population = juvenile_population + adult_population + senile_population



    print("Juvenile: ",juvenile_population)
    print("Adult: ",adult_population)
    print("Senile: ",senile_population)
    print("Total: ",total_population)
    counter += 1

A friend said to set new named variables, but then after one loop, won't you get the same problem again? I want the variables to update, but only after they've been printed, if that makes sense. Any suggestions?

Upvotes: 1

Views: 543

Answers (2)

michael_j_ward
michael_j_ward

Reputation: 4559

Per @Selcuk, you could use variable unpacking directly, but even with nicer formatting it looks unwieldly:

juvenile_population, adult_population, senile_population, total_population = (adult_population * birth_rate,
                                                                             juvenile_population * juvenile_survival,
                                                                             (adult_population * adult_survival) (senile_population * senile_survival), 
                                                                             juvenile_population + adult_population + senile_population)

My suggestion would be to either write a helper function, and keep "like" values in a dictionary like so:

populations = {'juvenile':  10,
               'adult':     10,
               'senile':    1
               }
survivals = {'juvenile':    1,
             'adult':       1,
             'senile':      0}
birth_rate = 2
generations = 5

def update_population(pops):
    juvie = pops['adult'] * birth_rate
    adults = pops['juvenile'] * survivals['juvenile']
    seniles = pops['adult'] * survivals['adult'] + (pops['senile'] * survivals['senile'])
    return {k:v for k,v in zip(['juvenile','adult','senile'],[juvie,adults,seniles])}

counter = 0
while counter < generations:
    populations = update_population(populations.copy())
    total_population = sum(populations.values())



    print("Juvenile: ",populations['juvenile'])
    print("Adult: ",populations['adult'])
    print("Senile: ",populations['senile'])
    print("Total: ",total_population)
    counter += 1

Upvotes: 0

Selcuk
Selcuk

Reputation: 59184

You are overwriting the existing values with new values. With Python you can merge all four lines into one like this:

juvenile_population, adult_population, senile_population, total_population = adult_population * birth_rate, juvenile_population * juvenile_survival, (adult_population * adult_survival) (senile_population * senile_survival), juvenile_population + adult_population + senile_population

This will assign all the values at once, without overwriting them first.

Upvotes: 1

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