04. Numbers, Strings, and Dictionaries

Exercise 1

In [1]:
4 ** 3  # output is int
Out[1]:
64
In [2]:
2 + 3.4 ** 2  # output is float
Out[2]:
13.559999999999999
In [3]:
(1 + 1j) ** 2  # output is complex
Out[3]:
2j

Exercise 2

In [4]:
# Define string
a = "Hello, egg world!"

# Find position of 'egg' word
pos = a.index('egg')

# Make new string
new_string = a[:pos] + a[pos+4:]

# Print out to check
print(new_string)

Hello, world!

Exercise 3

In [5]:
s = "CAGTACCAAGTGAAAGAT"
s.count("A")
Out[5]:
8
In [6]:
a = [1, 2, 3]
b = [4, 5, 6]
a + b
Out[6]:
[1, 2, 3, 4, 5, 6]

05. Booleans, Tuples, and Dictionaries

Exercise 1

In [7]:
x = 3.7
(x > 3.4 and x <= 6.6) or x == 2
Out[7]:
True

Exercise 2

In [8]:
words = {}
words['Table'] = 'Tisch'
words['Chair'] = 'Stuhl'
words['Snake'] = 'Schlange'
In [9]:
words['Chair']
Out[9]:
'Stuhl'

06. Control Flow

Exercise 1 and 2

In [10]:
for i in range(2, 51):  # just to 50 for this example

    # Set is_prime 'flag' to initial value
    is_prime = True

    # Try and divide i by all values between 2 and i-1, and if none of them
    # work, then the value is prime.
    for j in range(2, i):

        # Check if i is divisible by j
        if i % j == 0:
            is_prime = False
            break


    if is_prime:
        print(i)

2
3
5
7
11
13
17
19
23
29
31
37
41
43
47

There are other ways of doing this, e.g.:

In [11]:
for i in range(2, 51):
    for j in range(2, i):
        if i % j == 0:
            break
    else:  # this gets executed if break is not called
        print(i)

2
3
5
7
11
13
17
19
23
29
31
37
41
43
47

Exercise 2

In [12]:
a = 0
b = 1
while a < 100000:
    print(a)
    c = a  # save a to old variable
    a = b
    b = c + b

0
1
1
2
3
5
8
13
21
34
55
89
144
233
377
610
987
1597
2584
4181
6765
10946
17711
28657
46368
75025

Even simpler:

In [13]:
a, b = 0, 1
while a < 100000:
    print(a)
    a, b = b, a + b

0
1
1
2
3
5
8
13
21
34
55
89
144
233
377
610
987
1597
2584
4181
6765
10946
17711
28657
46368
75025

With a list:

In [14]:
fib = [0, 1]
while fib[-1] + fib[-2] < 100000:
    fib.append(fib[-1] + fib[-2])
print(fib)

[0, 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89, 144, 233, 377, 610, 987, 1597, 2584, 4181, 6765, 10946, 17711, 28657, 46368, 75025]