Solutions

How many paths?

The answer is B:

In [7]:
if 4 > 4:
    print('A')
elif 4 == 4:
    print('B')
elif 4 <= 4:
    print('C')

B

The condition 4 > 4 evaluates to False, while the conditions 4 == 4 and 4 <= 4 both evaluate to True. However because in our code the program would meet elif 4 == 4 first, it would execute the body contained in that branch. A program can only follow one branch in a conditional statement.

Close enough

A conditional statement that will perform this task is as follows:

In [8]:
a = 5.0
b = 5.1
if abs(b - a) < 0.1 * abs(a): 
#abs(a-b) is the absolute difference of a and b, and we want this to be less than 10% of a, 
#which we can obtain via abs(a)/10, or 0.1*abs(a)
    print('True')
else:
    print('False')

True

If you may have a different order of a and b from you neighbour then you may see different results with certain pairs of values.

Counting Vowels

The plan is for us to store all the vowels in one string vowels. Then when we are given another string sentence, we loop over the characters in sentence to see if they are in vowels, and thus are a vowel.

In [9]:
vowels = 'aeiouAEIOU'
sentence = 'Mary had a little lamb.'
count = 0 #this is how many vowels we found
for character in sentence:
    if character in vowels:
        #if we get to here, this character of sentence is also in vowels, so it's a vowel
        count += 1
    #we don't need an else, because we don't need to count the number of non-vowels
print("The number of vowels in this string is " + str(count))

The number of vowels in this string is 6

Nothing is true, everything is permitted

You can see the results below. You should notice that the statements are arranged into pairs, and they display a familiar pattern:

  • The empty string, or the string of zero length '' is considered False
  • Any non-empty string, or string of non-zero length is considered True
  • The empty list, or the list of zero length [] is considered False
  • Any non-empty list, or list of non-zero length is considered True
  • 0 is considered False
  • Any non-zero int is considered True
In [10]:
if '':
    print('empty string is true')
if 'word':
    print('word is true')
if []:
    print('empty list is true')
if [1, 2, 3]:
    print('non-empty list is true')
if 0:
    print('zero is true')
if 1:
    print('one is true')

word is true
non-empty list is true
one is true