02. Control Structures
Control Structures Review
Iteration with Loops
To iterate in Python, there are several options. A for loop can be used to iterate through a list or dictionary. Instead of the traditional for loop where we initialize a value i and increase / decrease it till it reaches an end value, Python's for loops are for-each in nature. This means that when you are iterating using a for loop over a list, you actually iterate over the items of that list.
If you also need the index values from the list while iterating, another possibility is to use enumerate, which is shown in an example below.
An additional way to iterate in Python is with a while loop. Just as in other programming languages, the while loop will repeat while some conditional statement is true. You will see more on conditional statements shortly, but first, here are examples of iteration with for and while loops.
# Examples of iteration with for loops.
my_list = [0, 1, 2, 3, 4, 5]
# Print each value in my_list. Note you can use the "in" keyword to iterate over a list.
for item in my_list:
print('The value of item is: ' + str(item))
# Print each index and value pair.
for i, value in enumerate(my_list):
print('The index value is: ' + str(i) + '. The value at i is: ' + str(value))
# Print each number from 0 to 9 using a while loop.
i = 0
while(i < 10):
print(i)
i += 1
# Print each key and dictionary value. Note that you can use the "in" keyword
# to iterate over dictionary keys.
my_dict = {'a': 'jill', 'b': 'tom', 'c': 'tim'}
for key in my_dict:
print(key + ', ' + my_dict[key])Remember that Python requires correct indentation for code blocks to be interpreted correctly. Indentation for a block is usually four spaces, or one tab length.
SOLUTION:
[0, 1, 2, 3]Conditional Statements
Conditional statements use boolean logic to help guide our decision process: the statement is true or false. These statements are structured using comparison operators: greater than (>), less than (<), and equal to (==).
Using conditional statements for control flow is accomplished in Python with the keywords: if, else, and elif. When doing multiple comparisons in Python, one after the other, the first comparison always usesif and the last comparison generally uses else. If additional control flow is needed, elif statements can be used; elif stands for "else if".
num = 5
if num < 5:
print('The number is smaller than 5.')
elif num == 5:
print('The number equals 5.')
else:
print('The number is greater than 5.')The code above would print: The number equals 5.
Control Structure Practice
In the following exercise you will finish writing smallest_positive which is a function that finds the smallest positive number in a list.
Exercise 1
Start Quiz:
User's Answer:
(Note: The answer done by the user is not guaranteed to be correct)
Exercise 2
Now let's assume you are planning on taking some additional courses at your local educational institution, and you have acquired some data about the available courses and when they will be offered. In the following exercise, you will write control structures to process the data and return the semesters when a given course is offered.
You will need to complete the function when_offered(courses, course). This function accepts a "courses" data structure and a "course" string. The function should return a list of strings representing the semesters when the input course is offered. See the two test cases below for examples of correct results.
Since the when_offered function accepts a dictionary data structure, you will find the
for <key> in <dictionary>:
<block>construct useful, as this loops through the key values in a dictionary.
Start Quiz:
User's Answer:
(Note: The answer done by the user is not guaranteed to be correct)