Create a class with functions in flutter and python 3.7 ready for Raspberry Pi as described in a document

Please check the document attached before post-proposal, all functions in this class must be completed as described with no bugs and good programming quality with the fastest way to solve the needed job, and with comments everywhere; this function reads a string and does equations if found, replaces variables if found, and does some logic if found then replace the founded and return the string or a variable or update a dictionary...etc. Or raise an expectation.

it shall be built on flutter dart and on python 3.7 (ready for Raspberry Pi)

both versions shall be delivered to mark this project as complete