The Python REPL (CLI)

https://en.wikipedia.org/wiki/Command-line_interface
Command-line interface

https://problemsolvingwithpython.com/
Problem Solving with Python (book).

CONCEPTS

Open and close the Python REPL
Compute mathematical calculations
Use variables in calculations
Import the math and statistics modules from the Python Standard Library and use their functions

INTRODUCTION

A command-line interface (CLI) processes commands to a computer program in the form of lines of text. The program which handles the interface is called a command-line interpreter or command-line processor.

An operating system CLI: UNIX/Linux (sh, ksh, csh, bash, tcsh, etc.), Windows (CMD.EXE, Power Shell).

An application CLI: Gnuplot, GNU Octave, MATLAB.

A language CLI: Python, Forth, LISP, Rexx, BASIC.

REPL (read-eval-print loop) or a language shell, is a simple interactive computer programming environment that takes single user inputs, executes them, and returns the result to the user. The Python REPL (the Python prompt) can be used as a calculator.

A command prompt (or just prompt) is a sequence of (one or more) characters used in CLI to indicate readiness to accept commands [Python (>>>), Linux ($ or #), Windows (>)].

DEBIAN 10

$ python             # run Python 2, the same for 'python2' or 'python2.7'
Python 2.7.16 (default, Oct 10 2019, 22:02:15) 
[GCC 8.3.0] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> 23 + 34     # comments after '#' are ignored
57
>>> _ + 12      # '_' (underscore) keeps the last result (read-only)
69
>>> a = 2 ; b = 5     # two statements are separated by ;
# results of assignments are not printed
>>> a * b
10
>>> 1 + 2 + \       # breaking the line with the backslash ...
... 4 - 3                     # ... continued
4
>>> (10 + 12 +     # open "(" or "[" or "{" is more readable
... 13)                     # ... continued
35
>>> [Ctrl]+[d]     # or quit(), the end of the work 
$                          # back to the shell

$ python3     # the same for 'python3.7'
Python 3.7.3 (default, Jul 25 2020, 13:03:44) 
[GCC 8.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> for i in [1, 2, 3]:   # a compound statement
...     print (i)
...                      # an empty line required
1
2
3
>>> import math      # math functions and constants
>>> help(math)       # exit with [q]
>>> help(math.sin)
>>> math.pi
3.1415926535897931
>>> math.sqrt(2) / 2.0   # using dot
0.70710678118654757
>>> [Ctrl]+[d]     # or quit(), the end of the work 
$                          # back to the shell

WINDOWS 10

Open 'Command Prompt' (cmd.exe) or 'Windows PowerShell' and run Python.