Circuit Python tutorials in Robotics II
View the Project on GitHub MrPrattASH/Robotics-II-Circuit-Python
In this tutorial, we’ll learn how to use conditional statements (if, elif, else) in CircuitPython to control the flow of our programs. Conditional statements allow us to execute certain pieces of code based on specific conditions.
Before we dive into conditional statements, let’s review variable types. In this course, we’ll work with four main types of variables:
0, 24, 4320.3, 435.4"Hello, world!" or single quotes 'Distance away is: 'True or Falseage = 15 # Integer
height = 5.7 # Float
greeting = "Hello!" # String
is_student = True # Boolean
and, or, not)Boolean expressions evaluate to a Boolean value (True or False). We use logical operators to create more complex Boolean expressions. The main logical operators are:
and: Returns True if both expressions are Trueor: Returns True if at least one expression is Truenot: Returns the opposite of the expression’s Boolean valuea = True
b = False
# 'and' operator example
print(a and b) # Output: False
# 'or' operator example
print(a or b) # Output: True
# 'not' operator example
print(not a) # Output: False
Write a small piece of code in your microcontroller’s code.py to test various combinations of Boolean and logical operators:
x = True
y = False
z = True
print(x and y) # False
print(x or y) # True
print(not z) # False
print(x and z) # True
print(y or z) # True
Conditional statements allow us to execute code only if specific conditions are met. Let’s explore the different types of conditional statements.
An if clause checks the condition and executes the body only if the condition is True. The structure looks like this:
if <condition>:
<body>
<condition>: The Boolean expression that is checked.<body>: The indented code block that runs if the condition is True.is_hot = True
if is_hot: # This condition is True, so the body below will execute
print("Take off your jacket!")
# We can also write
if is_hot == True:
print("Take off your jacket!")
# However, since is_hot = True, writing True == True is redundant.
Using your microcontroller, make my_condition a Boolean to display the three print statements in your serial console:
# vvv your code here
my_condition = True
# ^^^ your code here
if my_condition: # don't change this
print("You're doing...")
print("fantastic!!")
print(":)")
Expected Serial Output:
You're doing...
fantastic!!
:)
An if-else clause provides an alternative block of code that runs if the if condition is False. The structure looks like this:
if <condition>:
<body-1>
else:
<body-2>
<body-2>: The indented code block that runs if the condition is False.is_hot = False
if is_hot: # This condition is False, so the `else` body will execute
print("Take off your jacket!")
else:
print("Leave your jacket on.")
On your microcontroller, write an if-else statement where visitor_count is incremented if is_student is False:
is_student = False
visitor_count = 0
# Don't change the above code
# vvv write your code here
# ^^^ write your code here
# don't change the below code
print(visitor_count)
Expected Output:
Visitor Count: 1
Comparison operators are often used in conditional statements. Here are the main ones:
== (equals): Checks if two values are equal.!= (not equals): Checks if two values are not equal.< (less than): Checks if the left value is less than the right value.<= (less than or equals): Checks if the left value is less than or equal to the right value.> (greater than): Checks if the left value is greater than the right value.>= (greater than or equals): Checks if the left value is greater than or equal to the right value.a = 5
b = 10
print(a == 5) # True, because a is 5
print(a != 5) # False, because a is 5
print(a < 10) # True, because 5 is less than 10
print(a <= 5) # True, because 5 is equal to 5
print(a > 1) # True, because 5 is greater than 1
print(b >= 20) # False, because 10 is not greater than or equal to 20
In your microcontroller’s code.py, write and predict the output of these comparison statements:
x = 7
y = 3
print(x == y)
print(x != y)
print(x < y)
print(x <= 7)
print(x > y)
print(y >= 3)
Let’s use comparison operators in an if statement and create a practice exercise.
age = 16
if age >= 18:
print("You are an adult.")
else:
print("You are a minor.")
On your microcontroller, write a conditional statement using comparison operators to check the value of num. We should have 3 outputs:
"Greater than 10""Equal to 10""less than 10"num = 5
decision = ""
# Don't change the above code
# vvv write your code here
# ^^^ write your code here
# Don't change the below code
print(decision)
Expected Output:
Less than 10
An elif clause (short for “else if”) allows for multiple conditions to be checked in sequence. The structure looks like this:
if <condition-1>:
<body-1>
elif <condition-2>:
<body-2>
elif stands for “else if”.True.temperature = 30
if temperature > 40:
print("It's really hot!")
elif temperature > 30:
print("It's hot!")
else:
print("It's not hot.")
temperature = 35
if temperature > 40:
print("It's really hot!")
elif temperature > 30:
print("It's hot!") # This will execute because the condition is True
else:
print("It's not hot.")
On your microcontroller, write a conditional statement to check the variable is_allowed.
"Access granted""Access denied"is_allowed = False
message = ""
# Don't change the above code
# vvv write your code here
# ^^^ write your code here
# Don't change the below code
print(message)
Expected Output:
Access denied
You can combine if, elif, and else for more complex decision-making. The structure looks like this:
if <condition-1>:
<body-1>
elif <condition-2>:
<body-2>
else:
<body-3>
score = 85
if score >= 90:
print("Grade: A") # This will skip execution because `score >= 90` is false
elif score >= 80:
print("Grade: B") # This will execute because `score >= 80` is true
else:
print("Grade: C")
Using the code below as a template, write a selection statement that:
is_touched is True.
```python
is_touched = True # don’t change thisprint(“The touch sensor was pressed”)
## Practice Exercise #2
Using the code below as a template, write a selection statement that:
* an if/else statement that will print "touched"m if `is_touched` is `True`, and "non touched" if `is_touched` is `False`.
```python
is_touched = False # don't change this
# write your code here vvv
# write your code here ^^^
print("Touch sensor test complete")
Using the code below as a template, write a selection statement that:
print(“volume test complete”)
## Practice Exercise #4
*modified from [this](https://sites.google.com/view/circuitpython/tutorials/button-and-led/conditionals-i) tutorial*
* For this exercise, we've defined two variables, `eight_characters` and `contains_number` to check the strength of a password.
* Write a conditional statement that assigns a variable called `password_strength` depending on the following criteria:
* `password_strength = "Strong"` if a password has 8 characters and contains a number
* `password_strength = "Medium"` if a password has 8 characters or contains a number
* `password_strength = "Weak"` Otherwise, if a password contains neither 8 characters nor contains a number
* *Note: it is not required to actually **create** a password for this challenge, only to evaluate a hypothetical password based on the criteria*
Using the code below as a template, write a selection statement that will output a "Medium" print password strength string based on the criteria:
```python
eight_characters = True
contains_number = False
password_strength = ""
# Don't change the above code
# vvv write your code here
# ^^^ write your code here
# Don't change the below code
print(password_strength)
Expected Output:
Medium