Interactive Sessions

An interactive Python session lets you type one small piece of code and see the result immediately.

It is a scratch space, not a saved program. Use it when you want to ask Python a tiny question.

Start one with:

On macOS or Linux:

python3

On Windows PowerShell:

py -3

You will see a prompt like:

>>>

At that prompt, type:

2 + 3

The session prints:

5

The box below behaves like a small browser version of that prompt. It runs Python in your browser and keeps values from one command to the next.

A small Python prompt

Run an expression. Then try value = 10, followed by value * 2.

Python will start when you run the first command.

Ready to run.

Scripts and Sessions Are Different

In an interactive session, an expression can show its value:

In a script, the same expression usually produces no visible output unless you print it:

2 + 3

That script computes 5, but you do not see it. This visible difference causes confusion for beginners.

Use Sessions for Small Checks

Interactive sessions are useful for questions like:

  • What does this expression return?
  • How does this string method behave?
  • What is the type of this value?
  • What happens if I divide by zero?

They are not the best place for longer experiments. Once code becomes more than a few lines, put it in a script so you can save and rerun it.

A Quick Check

Try this:

The result tells you that 2 + 3 produced an integer.

You do not need to memorize every type name now. The habit matters more: ask Python small questions when you are unsure.

The Prompt Is Not Code

Do not paste the prompt itself into a script:

>>> 2 + 3

The >>> marker belongs to the interactive session. It is not Python code you write in a .py file.

Exercise: Prompt or code

Should >>> be included in a Python script?

Answer

Select one choice, then check.

HintSeparate interface from code

The interactive session displays >>> before you type. Ask whether Python or the programmer supplied those characters.

SolutionLeave out the prompt

Do not include >>> in a script. It is an interface marker displayed by the interactive session; the script contains only the code that follows it.

When to Use Each

Use an interactive session for tiny checks. Use a script when the code should be saved, rerun, shared, or inspected later.