very-cool-group

When adding functions or classes to a program, it can be tempting to reference inaccessible variables by declaring them as global. Doing this can result in code that is harder to read, debug and test. Instead of using globals, pass variables or objects as parameters and receive return values.

Instead of writing

def update_score():
    global score, roll
    score = score + roll
update_score()

do this instead

def update_score(score, roll):
    return score + roll
score = update_score(score, roll)

For in-depth explanations on why global variables are bad news in a variety of situations, see this Stack Overflow answer.

A REPL is an interactive shell where you can execute individual lines of code one at a time, like so:

>>> x = 5
>>> x + 2
7
>>> for i in range(3):
...     print(i)
...
0
1
2
>>>

To enter the REPL, run python (py on Windows) in the command line without any arguments. The >>> or ... at the start of some lines are prompts to enter code, and indicate that you are in the Python REPL. Any other lines show the output of the code.

Trying to execute commands for the command-line (such as pip install xyz) in the REPL will throw an error. To run these commands, exit the REPL first by running exit() and then run the original command.