Course on Internet of Things

Exercises Session 1:

Introductory remarks:

The scripts we are going to develop during this exercise session do not depend on any system issues: We do not use command line arguments not available in MicroPython nor do we use any hardware specific features which are not available on a PC. The exercises can therefore be developed and run on the ESP32 but also on any standard PC with Python3 installed.

Exercise 1: Use of REPL

Connect to your ESP32 with minicom or thonny. You may try the same thing running Python3 on your PC.

Using REPL:

• print “Hello World!”

• read in a text using input() and print it

• Calculate

  

• Calculate sin(30°)
  If you see errors, how do you correct them? Are the results correct?

• Finally make the "print Hello World!" command a script and execute it.

Exercise 2: A simple calculator

Write a script that assigns the values 5 and 3 to the variables a and b respectively

Print the results of 4 basic arithmetic operations:

• a+b

• a-b

• a*b

• a/b

If you use integer format when printing the result, you will see the result truncated to an integer. Can you correct changing the format?

https://iotworkshop.africa/pub/IoT_Course_English/REPLAndStandardPythonProgramming/calculatorV1.py.txt

Improve this program asking the user to enter 2 real numbers (floats) separated by a space. This is how it should look like:

If this happens:

when the user mistypes and enters something that is not a real number, can you capture the error and simply ask the user to repeat his input, until you get 2 correct floating point numbers?

https://iotworkshop.africa/pub/IoT_Course_English/REPLAndStandardPythonProgramming/calculatorV2.py.txt

Bonus points: Writing a parser for user input is rather easy if the numbers and operator are separated by spaces (have a look at the split method of strings). It is quite a bit more tricky if you allow entering calculations without spaces between the operands and the operator. Can you write a parser accomplishing this?

Hint: A very elegant solution to this is the use of regular expressions and Python provides a module helping you with this:

https://docs.micropython.org/en/latest/library/ure.html

A float is defined as follows:

• zero or more spaces

• followed by one '+' or one '-'
• followed by
  • a ‘.’ followed by at least one digit
• or
  
  • at least one digit followed by zero or one ‘.’ followed by zero or more digits

• followed be zero of more spaces

Try your parser on this input:

Input	ok or not ok
5.3+4.7	ok
5.3++4.7	not ok
5..3 + 4.7	not ok
.3+.7	ok
5.3+4b7	not ok
empty string	not ok
5.3+.	not ok
5.3+	not ok
-1--1	ok
--1--1	not ok

Try also several spaces in between operands and operator.

https://iotworkshop.africa/pub/IoT_Course_English/REPLAndStandardPythonProgramming/calculatorV3.py.txt

Exercise 3: Conditions

Like in exercise2, start with 2 numbers a,b with values 5 and 7. In your program check which of the 2 numbers is bigger and print the result.

Then improve the program asking the user for 2 integer numbers. Make sure he enters 2 correct numbers and capture possible errors. This is a typical output:

Exercise 4: The Fibonacci series

The Fibonacci number series is defined as:

F(0) = 0; F(1) = 1

F(n) = F(n-1) + F(n-2)

• Calculate and print out the Fibonacci numbers up to F(n). Get n from the user where n >= 0

Try your program for n=0, n=1, n=2, n=3, n=20

• Ask the user up to which is the maximum number up to which you should calculate.

Exercise 5: A bit of Mathematics: Calculate the sine function

Write a script that asks the user for an angle in degrees. Calculate the sine of this angle.

Exercise 6: Classes

Write a Python class with methods calculating mathematical number series. These series should be calculated:

• The Fibonacci numbers up to F(n). n is passed as parameter to the method
• The Fibonacci numbers smaller than max. max is passed as parameter to the method
• The prime numbers up to max
• Factorial:
  
• The geometric number series:
  
• The harmonic number series:
  
  Can you tell what the following series calculate?

Add these series to your class and try. Write a test script exercising the different methods.

Please also have a look at the Wikipedia page on number series: https://en.wikipedia.org/wiki/Series_(mathematics)

In order to make this exercise run on the ESP32 you must first upload your mathSeries.py module implementing the MathSeries class into the file system of the ESP32. Create a directory called lib on the ESP32 file system and put your module there:

ampy mkdir /lib

ampy put mathSeries.py /lib/mathSeries.py

Once this is done, go to the REPL window of thonny and

import mathSeries

You can now create an instance of the MathSeries class:

series = mathSeries.MathSeries()

When running on a PC you may want to plot the series as well. If you don't know how to plot data in Python, you will find all the information needed here:
https://matplotlib.org/3.2.1/index.html

Here is the exercise sheet in odt format:

https://iotworkshop.africa/pub/IoT_Course_English/REPLAndStandardPythonProgramming/exercise_1.odt

-- Uli Raich - 2020-05-03

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