Expanding on a problem from Automate the Boring Stuff

Question

Note: this is not the solution for the "Character Picture Grid" problem from Automate the Boring Stuff. Instead, this is an expansion of that problem simply for the sake of understanding nested loops, lists within lists, and iterating through values in order to print a picture on the screen.

Thanks to anyone who takes the time to review this. Should I comment more throughout my code so that it's easier to read? Are there ways to shorten this program so that it could run faster? I'm still quite new to programming.

# This is an expanded version of the Character Picture Grid
# problem from Al Sweigart's book, Automate the Boring Stuff With Python.
# This function takes in user input to determine what direction to print
# the arrow.

rightArrow = [['.', '.', '.', '.', '.', '.'], 
              ['.', 'O', 'O', '.', '.', '.'],
              ['O', 'O', 'O', 'O', '.', '.'], 
              ['O', 'O', 'O', 'O', 'O', '.'],
              ['.', 'O', 'O', 'O', 'O', 'O'], 
              ['O', 'O', 'O', 'O', 'O', '.'],
              ['O', 'O', 'O', 'O', '.', '.'], 
              ['.', 'O', 'O', '.', '.', '.'],
              ['.', '.', '.', '.', '.', '.']]


def printArrow(list):
    rowLength = len(list[0])  # length of x plane coordinates
    columnLength = len(list)  # length of y plane coordinates
    print('Welcome to Arrow Pointer v1.0!')
    while True:
        #main program loop
        print('\n\nType in one of the following:\n\nup, down, left, right, or end to exit the program.')
        #user determines direction of arrow to be printed
        userInput = input()
        if userInput.lower() == 'right':
            for i in range(columnLength):
                for j in range(rowLength):
                    #first loop iterates through main list
                    #nested loop iterates through inner list elements
                    print(list[i][j] + '     ', end='')
                print('\n')

        if userInput.lower() == 'left':
            for i in range(columnLength):
                for j in range(rowLength - 1, -1, -1):
                    #iterate backwards to print arrow in opposite direction
                    print(list[i][j] + '     ', end='')
                print('\n')

        if userInput.lower() == 'down':
            for i in range(rowLength):
                for j in range(columnLength):
                    print(list[j][i] + '     ', end='')
                print('\n')

        if userInput.lower() == 'up':
            for i in range(rowLength-1, -1, -1):
                for j in range(columnLength-1, -1, -1):
                    print(list[j][i] + '     ', end='')
                print('\n')

        if userInput.lower() == 'end':
            quit()

printArrow(rightArrow)

Answer 1

• Let's start with the basics. Always use if __name__ == "__main__": printArrow(rightArrow) instead of directly calling your function (printArrow(rightArrow)) to avoid running it if importing the function in the future from another module.
• A function called printArrow should print an arrow, not ask a user for input, print an arrow, and control the flow of the program. Divide it into def print_arrow(list, direction), main(), etc.
• Instead of using quit() which controls the global execution flow, you can use a plain return when inside a function. Cleaner and follows SRP.
• Naming! In python we don't usually use camelCase for functions; use instead: print_arrow. Same for variables like rowLength -> row_length.
• Pass your code through black or similar to have it nicely formatted (black.vercel.app/), otherwise the small human "errors" show up :)
• Constants in Python, by convention, use all upper case and don't need to be passed into functions (the only exception when globals are generally acceptable). So use rightArrow -> RIGHT_ARROW and def printArrow(list): -> def printArrow():.
• Use comments for the important stuff (the one which I can't trivially deduce from the code itself). What is this arbitrary amount of spaces? ' '? Put it into a constant and comment why that many if it has a meaning. E.g., SEPARATOR = ' '.
• There is some code repetition, can't you put this into a function def _print_arrow_auxiliary(x_start: int, x_end: int, x_step: int, y_start: int, y_end: int, y_step: int) -> None:?

for i in range(rowLength-1, -1, -1):
    for j in range(columnLength-1, -1, -1):
        print(list[j][i] + '     ', end='')
    print('\n')

• It is a matter of taste, but type-hinting your functions does give you many advantages (self-explanatory code, better IDE highlights and suggestions, etc.)... def printArrow(list): -> def printArrow(list: List[List[str]]) -> None:.