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Engineering LibreTexts

4.10: Using Constant Variables Instead of Strings

  • Page ID
  • DONUT = 'donut'
    SQUARE = 'square'
    DIAMOND = 'diamond'
    LINES = 'lines'
    OVAL = 'oval' 

    The program also sets up constant variables for some strings. These constants will be used in the data structure for the board, tracking which spaces on the board have which icons. Using a constant variable instead of the string value is a good idea. Look at the following code, which comes from line 187:

    if shape == DONUT:

    The shape variable will be set to one of the strings 'donut', 'square', 'diamond', 'lines', or 'oval' and then compared to the DONUT constant. If we made a typo when writing line 187, for example, something like this:

    if shape == DUNOT:

    Then Python would crash, giving an error message saying that there is no variable named DUNOT. This is good. Since the program has crashed on line 187, when we check that line it will be easy to see that the bug was caused by a typo. However, if we were using strings instead of constant variables and made the same typo, line 187 would look like this:

    if shape == 'dunot':

    This is perfectly acceptable Python code, so it won’t crash at first when you run it. However, this will lead to weird bugs later on in our program. Because the code does not immediately crash where the problem is caused, it can be much harder to find it.