ungleich-learning-circle/balazs/python-calculator/notes.org

• Python applying learnings from 1..6
  • Lecture notes
• State:

Python applying learnings from 1..6

Lecture notes

• Previous topics covered:

  • Printing
  • Formatting
  • Variables
  • Escape Sequences
  • Inputting text
  • Reading arguments / using argv
  • Reading files
  • Defining methods
  • Boolean logic
  • Branching using if/else/elif
  • Loops: for/while

• Today we write a calculator that saves results in a file in python

  • How it works in general You read the input until you read a line that only contains a "q". Every input line consists of numbers separated by a space. For instance "4 5 9". You will need to .split() the input.

• Steps

  • Create a python script named "calc.py"

  • It takes 1 command line argument (argv), which is the filename

    • We will store the calculations and results in this file

  • Create a method named "input_and_calculate_one_line"

    • It does not have any arguments
    • It reads one line via input
    • It splits the input (let's say "4 5 9" => [ "4", "5", "9") ])
    • It calculates the result (f.i. 4+5+9 = 18) and stores it in a variable (use sum over the list)
    • It returns a string of the format "4 + 5 + 9 = 18"
    • If the line only contains a "q" it return "" (an empty string)

  • Create a method named "editor" that takes a filename as an argument

    • It opens the file for writing
    • It uses input_and_calculate_one_line in a while loop
    • while the return result is not "", we append the string to the file
    • When the return result is "", the function exits

State:

input_and_calculate_one_line is complete, however it's probably a garbage implementation. Spent too much time on converting back and forth and getting the output right.

Editor (file io) is not complete yet