Solutions to Exercise 1: REPL and standard Python programming

Exercise 1: Use of REPL

The screen shot shows the REPL session

Exercise 2: A simple calculator

In the first example we use fixed values for the calculations. To print out the results I first use integer (%d) format and then floating point format (%f) to get the division right.

https://iotworkshop.africa/pub/IoT_Course_English/SolutionsToREPLAndStandardPythonProgramming/assignments.py.txt

In the second example I define 4 functions for the 4 basic arithmetic operations. The dictionary with the operator as key and the function as value allows me to select the function to be called depending on the operator given. I write a simple parser to check that user input is correct. Since I force a space between operands and operator it becomes easy to split the calculation into 3 tokens: 2 operands and the operator. Now all I need to do is converting the operator strings to floating values and call the corresponding function.

https://iotworkshop.africa/pub/IoT_Course_English/SolutionsToREPLAndStandardPythonProgramming/calculator.py.txt

The last example is quite a bit more tricky as I cannot use the string method split to separate operands and operator any more. The parser allows the characters 0..9,"." and "+","-","*","/".

The operator may only consist of 1 or more digits and/or the decimal point. It may not contain more than 1 decimal point and it must contain at least 1 digit. The operator can be only one of the above basic arithmetic operators. Here is my solution. Test it yourself and try to find an illegal character combination that is not treated. Error handling is often the most difficult part of a program!

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

-- Uli Raich - 2020-05-03

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