It's like this: Python leads a double life. It's an interpreter for scripts that you can run from the command line or run like applications, by double-clicking the scripts.
What is Interactive Shell
But it's also an interactive shell that can evaluate arbitrary statements and expressions. This is extremely useful for debugging, quick hacking, and testing.
I even know some people who use the Python interactive shell in lieu of a calculator!
Launch the Python interactive shell in whatever way works on your platform, and let's dive in with the steps shown here:
First Steps in the Interactive Shell
>>> 1 + 1 ❶
>>> print 'hello world' ❷
>>> x = 1 ❸
>>> y = 2
>>> x + y
❶ The Python interactive shell can evaluate arbitrary Python expressions, including any basic arithmetic expression.
❷ The interactive shell can execute arbitrary Python statements, including the print statement.
❸ You can also assign values to variables, and the values will be remembered as long as the shell is
open (but not any longer than that).