21 - Functions III - returning values.ipynb

Kernel: Python 3 (system-wide)

Exercise 21.1

Modify your code from Exercise 20.2 so that the function average() returns the average of a list of numbers rather than printing it.

arriving_penguins = [10, 156, 73, 376, 786, 432, 1035, 901, 1102, 2567, 1571, 916, 1560, 632, 943, 246, 654, 1456, 504, 632]

def average(x):
    '''Average of a list of numbers'''
    return sum(x)/len(x)

arriving_penguins = [10, 156, 73, 376, 786, 432, 1035, 901, 1102, 2567, 1571, 916, 1560, 632, 943, 246, 654, 1456, 504, 632]

ave = average( arriving_penguins )
print(ave)

Exercise 21.2

1. Write a function that takes the following list of individual lemur species as an argument, creates a dictionary of the number of sightings of each lemur species and returns that dictionary.

2. Print out each species name and its number of sightings in descending order of sightings.

   • Hint: You wrote the code for counting lemur sightings in Exercise 17.1. Copy and paste that code then modify it.

lemurs = ['White-headed lemur', 'Gray-headed lemur', 'Common brown lemur', 'Collared brown lemur', 'Red lemur', 'Collared brown lemur', 'Red-fronted lemur', 'Red-bellied lemur', 'Collared brown lemur', 'Crowned lemur', 'Red lemur', 'Crowned lemur', 'Blue-eyed black lemur', 'Common brown lemur', 'Mongoose lemur', 'Common brown lemur', "Sanford's brown lemur", 'White-headed lemur', 'Black lemur', 'Mongoose lemur', 'Red-bellied lemur', 'Red-fronted lemur', 'Blue-eyed black lemur', 'Collared brown lemur', 'Blue-eyed black lemur', 'White-headed lemur', 'Red lemur', 'Red-bellied lemur', 'Gray-headed lemur', 'Red-bellied lemur', 'Red lemur', 'Common brown lemur', 'Mongoose lemur', 'Red lemur', 'Common brown lemur', "Sanford's brown lemur"]

def count_lemurs(lemurs):
    '''Count the number of sightings of each lemur species'''
    sightings = {}

    for lemur in lemurs:
        if lemur not in sightings:
            sightings[lemur] = 1
        else:
            sightings[lemur] += 1

    return sightings

lemur_count = count_lemurs(lemurs)

for species, count in sorted(lemur_count.items(), reverse=True, key=lambda kv: kv[1]):
    print( f'{species}\t{count}')

Exercise 21.3

In Exercise 18.3 you calculated the molecular mass of the peptide "FWGCYPT".

Write a program that passes a peptide sequence to a function called peptide_mass and return its molecular mass.

masses = {
    'A' : 71.03711,
    'C' : 103.00919,
    'D' : 115.02694,
    'E' : 129.04259,
    'F' : 147.06841,
    'G' :  57.02146,
    'H' : 137.05891,
    'I' : 113.08406,
    'K' : 128.09496,
    'L' : 113.08406,
    'M' : 131.04049,
    'N' : 114.04293,
    'P' :  97.05276,
    'Q' : 128.05858,
    'R' : 156.10111,
    'S' :  87.03203,
    'T' : 101.04768,
    'V' :  99.06841,
    'W' : 186.07931,
    'Y' : 163.06333}

def peptide_mass(peptide):
    '''calculate the molecular mass of peptide'''
    mass = 0

    for aa in peptide:
        mass += masses[aa]

    return mass

for peptide in ['CPHRALIAIT', 'NGQSVCGMSG', 'WPFYWRICNH', 'DLQVIDQMNW', 'CEWIMYVTDE']:
    print(f'Mass of {peptide} is {peptide_mass(peptide):.5f} Daltons')

Exercise 21.4

Write a function that splits someone's full name into a forename and surname and returns both of these separately.

• Hint: In Exercise 7.3 you split a string of two sentences into two separate sentences. Use the same technique here but split on a space rather than a full stop.

full_names = ['Harry Potter', 'Hermione Granger', 'Ronald Weasley']

def split_name(full_name):
    '''Split a full name into forename and surname'''
    idx = full_name.find(' ')
    forename = full_name[:idx]
    surname = full_name[idx+1:]
    return forename, surname

for name in full_names:
    forename, surname = split_name(name)
    print(f'{surname.upper()} {forename}')