Python is an interpreted language, and code is evaluated line-by-line. Since each line can be evaluated by itself, the time between evaluating each line doesn't matter, and this allows us to have a REPL.
REPL stands for: Read, Evaluate, Print, Loop
Each line is read and evaluated. The return value is then printed to the screen, and then the process repeats.
Python ships with a REPL, accessible by running
python3.7 from a terminal.
$ python3.7 Python 3.7.2 (default, Jan 15 2019, 19:31:18) [GCC 4.8.5 20150623 (Red Hat 4.8.5-36)] on linux Type "help", "copyright", "credits" or "license" for more information. >>>
>>> indicates a line to type in, like a command prompt for Python. Later on we'll see a
..., which means that we are currently sitting in a scoped area. The only way out is to enter a blank line (no spaces) before the interpreter will evaluate the entire code block.
The simplest use of this would be to do some math:
>>> 1 + 1 2 >>>
2 is the return value of the expression and it is then printed to the screen. If something doesn't have a return value, then nothing will be printed to the screen and we'll just land back at a
>>> prompt. We'll cover this later, but an example would be
>>> None >>>
To exit the REPL, we can either type
exit() (the parentheses are important) or hit
Ctrl+d on your keyboard.