Population growth

Define a function population_growth that receives an initial population,
annual rate of growth, and target population. Use a while loop to calculate
how many years it takes to go over the target population and return it. If
the annual growth rate is not greater than zero, return 'invalid growth rate'.
Do not use math.pow or the x**y operator.

Target = Initial * (1 + rate)^(number of years)

Examples:

>>> population_growth(5000, 0.1, 10000)
8
>>> population_growth(5000, 0.1, 20000)
15
>>> population_growth(5000, 0.1, 40000)
22
>>> population_growth(5000, 0, 40000)
'invalid growth rate'

Test Cases

test population X2 - Run Test

def test_population_X2():
    assert population_growth(5000, 0.1, 10000) == 8

test population X4 - Run Test

def test_population_X4():
    assert population_growth(5000, 0.1, 20000) == 15

test population X8 - Run Test

def test_population_X8():
    assert population_growth(5000, 0.1, 40000) == 22

test bad growth rate - Run Test

def test_bad_growth_rate():
    assert population_growth(5000, 0, 40000) == 'invalid growth rate'

Recorded solution

Population growth Lesson - Base Python Track

Solution 1

def population_growth(initial_pop, annual_growth_rate, target_pop):
    # Initial check, let's make sure it's a valid growth rate
    if annual_growth_rate <= 0:
        return 'invalid growth rate'

    # All good! Let's start the actual algo:
    
    current_pop = initial_pop
    num_years_passed = 0
    while current_pop <= target_pop:
        current_pop *= (1 + annual_growth_rate)
        num_years_passed += 1
    return num_years_passed

Files associated with this lesson:

Population Growth Explanation.ipynb

Population Growth¶

Initial population: 5,000
Growth Rate: 0.1
Target Population: 10,000

In [1]:

initial = 5_000
growth_rate = 0.1
target = 10_000

In [6]:

current = initial

Year 1

In [7]:

new_people = current * growth_rate


current = new_people + current
current

Out[7]:

5500.0

Year 2

In [9]:

new_people = current * growth_rate
new_people

current = new_people + current
current

Out[9]:

6050.0

Year 3

In [10]:

new_people = current * growth_rate
new_people

Out[10]:

605.0

In [11]:

current = new_people + current
current

Out[11]:

6655.0

Year 4

In [12]:

new_people = current * growth_rate
new_people

Out[12]:

665.5

In [13]:

current = new_people + current
current

Out[13]:

7320.5

Year 5

In [14]:

new_people = current * growth_rate
new_people

Out[14]:

732.0500000000001

In [15]:

current = new_people + current
current

Out[15]:

8052.55

Year 6

In [16]:

new_people = current * growth_rate
new_people

Out[16]:

805.2550000000001

In [17]:

current = new_people + current
current

Out[17]:

8857.805

Year 7

In [18]:

new_people = current * growth_rate
new_people

Out[18]:

885.7805000000001

In [19]:

current = new_people + current
current

Out[19]:

9743.585500000001

Year 8

In [20]:

new_people = current * growth_rate
new_people

Out[20]:

974.3585500000002

In [21]:

current = new_people + current
current

Out[21]:

10717.944050000002

In [25]:

target

Out[25]:

In [26]:

current

Out[26]:

10717.944050000002

In [27]:

current < target

Out[27]:

False

In [35]:

current = 5_000

In [36]:

def population_growth(initial_pop, annual_growth_rate, target_pop):
    years = 0
    while current < target:
        new_people = current * growth_rate
        current = new_people + current
        years += 1
    return years

Population growth

Test Cases

Files associated with this lesson:

Population Growth¶

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