Exercise 001¶

Variables and Printing¶

Store the string Hello World in a variable with name first_variable and print it.

In [1]:

first_variable = "Hello World"

first_variable = "Hello World"

For-Loops¶

Count from 1 to 10 by using a for loop, store each value in a variable value and print it. Use the range-function to help you.

Tip: Typically programming languages start by counting from zero. Make sure that the range-function starts correctly.

In [2]:

for number in range(0, 11):
  print(number)

for number in range(0, 11): print(number)

0
1
2
3
4
5
6
7
8
9
10

While-Loops¶

Repeat the previous task using a while-loop.

Tip: While-Loops are closed by a condition, so make sure that the loop is stopped at the end.

In [3]:

number = 0
while number <= 10:
  print(number)
  number += 1

number = 0 while number <= 10: print(number) number += 1

0
1
2
3
4
5
6
7
8
9
10

Conditional statements¶

Count from 1 to 10 using a for-loop, store each value in variable value and distinguish whether a number is odd or even. Print each result and modify the print to display whether the number is odd or even as well as the number itself:

Example:

print("odd", 1)

Tip: Use the modulo-function using the %-operator. It behaves similar to any other operator and returns the remainder of the division.

5 % 5 = 0

In [4]:

for number in range(0, 11):

  if number % 2 == 0:
    print("even", number)
  else:
    print("odd", number)

for number in range(0, 11): if number % 2 == 0: print("even", number) else: print("odd", number)

even 0
odd 1
even 2
odd 3
even 4
odd 5
even 6
odd 7
even 8
odd 9
even 10

Lists #1¶

Store the numbers 1 to 5 in a list under the variable my_list and print it. Finally, add the first and last element of the list and print the result.

In [5]:

my_list = []

for number in range(1, 11):
  my_list.append(number)

print("Addition of first and last: ", my_list[0] + my_list[-1])

my_list = [] for number in range(1, 11): my_list.append(number) print("Addition of first and last: ", my_list[0] + my_list[-1])

Addition of first and last:  11

Lists #2¶

Store the number 0 to 49 in a list under variabl my_list. Now sort the list in two new lists even and odd, where each list contains even and odd number from my_list respectively. Finally, print both lists.

Tip: So called list comprehensions unify the concept of a list and a for-loop into a single line. In addtion, you can add conditions that help only to include those value in a list, that meet the conditions.

In [6]:

# Using list comprehension
numbers = [number for number in range(0, 50)]

even, odd = [], []

for number in numbers:
  if number % 2 == 0:
    even.append(number)
  else:
    odd.append(number)

print("Even numbers: ", even)
print("Odd numbers: ", odd)

# Using list comprehension numbers = [number for number in range(0, 50)] even, odd = [], [] for number in numbers: if number % 2 == 0: even.append(number) else: odd.append(number) print("Even numbers: ", even) print("Odd numbers: ", odd)

Even numbers:  [0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48]
Odd numbers:  [1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49]

Dictionaries¶

Store both of the previous lists even and odd in a dictionary by mapping each list using the keys even and odd. In addition, add a new list which contains all numbers in my_list that are divisible by 3 using the dictionary key by_three. Finally, print the dicitonary to inspect its content.

In [7]:

import rich # This just for an overview, you can ignore it

division_dict = {
    "odd": odd,
    "even": even,
    "by_three": [number for number in numbers if number % 3 == 0]
}

rich.print("Resulting dictionary: ", division_dict)

import rich # This just for an overview, you can ignore it division_dict = { "odd": odd, "even": even, "by_three": [number for number in numbers if number % 3 == 0] } rich.print("Resulting dictionary: ", division_dict)

Resulting dictionary: 
{
    'odd': [1, 3, 5, 7, 9, 11, 13, 15, 17, 19, 21, 23, 25, 27, 29, 31, 33, 35, 37, 39, 41, 43, 45, 47, 49],
    'even': [0, 2, 4, 6, 8, 10, 12, 14, 16, 18, 20, 22, 24, 26, 28, 30, 32, 34, 36, 38, 40, 42, 44, 46, 48],
    'by_three': [0, 3, 6, 9, 12, 15, 18, 21, 24, 27, 30, 33, 36, 39, 42, 45, 48]
}

Reading and writing of files (Optional)¶

Write out all numbers found in even to a file called even.txt. Next, read the same file and save the result in a new list called new_list. Finally, add the first and third entry of the list. Does it work? If not, can you find an explanation?

Tip: When writing to a file, Python does exactly what its told. So make sure to include newlines \n after writing each number. Otherwise, reading it correctly will be impossible.

Tip: Newlines \n will also be read and can be removed upon parsing of a line by using line.strip(), where line is the string on which you'd like to remove the newline.

Tip: Using the open-function facilitates writing and reading of a file. There are ways to shorten your work. See the following examples:

# Write to a file
with open("example.txt", "w") as file:

    for value in my_list:
        file.write("Example")

# Read from a file
example = [ line.strip() for line in open("example.txt", "r").readlines() ]

In [9]:

# Writing the file
with open("even.txt", "w") as f:
  for number in even:
    f.write(f"{number}\n")

# Reading the file (using a list comprehension)
my_list = [line.strip() for line in open("even.txt").readlines()]

print("Addition of first and last: ", my_list[0] + my_list[-1])
print("Entry types: ", type(my_list[0]))

# We need to modify our code!
my_list = [
    int(line.strip()) # Type-cast to an integer
    for line in open("even.txt").readlines()
]

print("\nType casted - Addition of first and last: ", my_list[0] + my_list[-1])
print("Entry types: ", type(my_list[0]))

# Writing the file with open("even.txt", "w") as f: for number in even: f.write(f"{number}\n") # Reading the file (using a list comprehension) my_list = [line.strip() for line in open("even.txt").readlines()] print("Addition of first and last: ", my_list[0] + my_list[-1]) print("Entry types: ", type(my_list[0])) # We need to modify our code! my_list = [ int(line.strip()) # Type-cast to an integer for line in open("even.txt").readlines() ] print("\nType casted - Addition of first and last: ", my_list[0] + my_list[-1]) print("Entry types: ", type(my_list[0]))

Addition of first and last:  048
Entry types:  <class 'str'>

Type casted - Addition of first and last:  48
Entry types:  <class 'int'>