https://en.wikipedia.org/wiki/Command-line_interface
Command-line interface
https://problemsolvingwithpython.com/
Problem Solving with Python (book).
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 (>)].
$ python # run Python 3, the same for 'python3' or 'python3.13'
Python 3.13.5 (main, Jun 25 2025, 18:55:22) [GCC 14.2.0] on linux
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
>>> 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
3.141592653589793
>>> math.sqrt(2) / 2.0 # using dot
0.7071067811865476
>>> [Ctrl]+[d] # or quit(), the end of the work
$ # back to the shell
Open Command Prompt (cmd.exe) or Windows PowerShell and run Python.