FMDA Excercise 4.2

#%% Exercise on population 4_2
"""
Assignment:
    1  download file
    2  calculate pop change P[d] 'Population delta'
    3  calculate pop growth rate 'r' in % on yearly basis (see calculation below)
       r = P[d] / ( P[t-1] * t[d] )
    4a print a table; headers & data
    4b print a sequence of lines that read;
       - Time period (initial year (t0) – final year (t1)).
       - Initial population (million) at t0.
       - Population change (million) <-- your results.
       - Population growth rate (%) <-- your results.
"""

file_name = "your file name.dat"
file_path1 = "your file path"
file_path2 = "your alternative file path"
file_path_complete1 = file_path1 + file_name
file_path_complete2 = file_path2 + file_name


line_data = 0 # emty this string before starting
tab_char = 0 # location of tab
prev_line_read = str() # empty string befrore starting
pop_list = [] # list of population
year_list = [] # list of year
pop_incr = 0 # population increase per timestep
a = 0 # iteration value for making lists (used multiple times)
p_incr_list = [] # list of population increase per timestep
growth_rate = 0 # speaks for itself
r_list = [] # list of growthrates



#open file
try:
    file_data = open(file_path_complete1, "r")
except:
    try:
        file_data = open(file_path_complete2, "r")
    except:
        print("Open Failed!")

# read data into list of population and year (and close file)
while True:
    line_read = file_data.readline()
    try: # Check if line is data or something else (header or end)
        line_data = int(line_read[:1]) + 1
        tab_char = line_read.find("\t", 1)
        line_read_len = len(line_read) - 1

        population = int(line_read[tab_char + 1:line_read_len])
        pop_list.append(population)
        year = int(line_read[:tab_char])
        year_list.append(year)
    except:
        if line_read == "":
            break
file_data.close()

# print lists as check
#print(year_list, "\n")
#print(pop_list, "\n")

#(step 2) make list of population increase per timestep
for i in pop_list:
    if a != 0:
        b = a - 1
        pop_incr = (pop_list[a]) - (pop_list[b])
        p_incr_list.append(pop_incr)
    else:
        p_incr_list.append(0)
    a = a + 1

# print list as check
#print(p_incr_list, "\n")

#(step 3) calculate growthrate 'r'
a = 0
for i in pop_list:
    if a != 0:
        b = a - 1
        growth_rate = p_incr_list[a] / ( pop_list[b] * ( year_list[a] - year_list[b] ) )
        growth_rate = round(growth_rate, 4)
        r_list.append(growth_rate)
    else:
        r_list.append(0)
    a = a + 1

# print list as check
#print(r_list, "\n")

#(step 4a) print a table
print("Year\tPopulation\tPop. increase\tGrowth rate")
a = 0
for i in pop_list:
    print(year_list[a], "\t", pop_list[a], "\t", p_incr_list[a], "\t", r_list[a])
    a = a + 1

#(step 4b) print line sequence
print("\n- Time period ", year_list[0], " to ", year_list[len(year_list)-1])
population = round(float(pop_list[0])/1000,1)
print("- Initial population", population, " (million) at year ", year_list[0])
pop_change = round(float((pop_list[len(pop_list)-1] - pop_list[0]))/1000, 1)
print("- Population change ", pop_change, " (million)")
growth_rate = round(float( sum(p_incr_list) / ( pop_list[0] * ( year_list[len(year_list)-1] - year_list[0] ) ))*100,2)
print("- Population growth rate ", growth_rate, "% (yearly average)")