# The Basics¶

Throughout the class, we’re going to do a lot of hands-on, dive-in, figure-it-out-along-the-way work. There’s a good chance you’ll have a lot of moments when you don’t know exactly what’s going on, and that’s okay! I want to keep your hands on they keyboard, and your mind working hard. If you get stuck, don’t worry, I’m here to help.

## REPL¶

As we jump right in, we’re going to start with typing code at the **Python REPL**.

REPL stands for **Read-Execute-Print Loop**, but don’t worry about remembering that. What you *should* remember is that the Python REPL (sometimes called the Python shell or Python command prompt) is a place where we can do quick and dirty Python-y stuff. It’s great for testing things out, and getting familiar with how Python works.

To start the REPL, open up a command/terminal window. In your command/terminal window, type:

```
$ python3.6
```

This will start the REPL. You can tell when you are in the REPL because the prompt will change to be `>>>`

.

Note

If you’re on Windows and `python3.6`

doesn’t work, try `py3.6`

.

We can type code in the Python REPL and once we hit `Enter`

Python will execute our code and print out the result.

## Arithmetic¶

Let’s look at some basic math:

```
>>> 2 + 2
4
```

Python has numbers and arithmetic, just like every other programming language.

You can add integers. You can add floating point numbers.

```
>>> 2 + 2
4
>>> 1.4 + 2.25
3.65
```

You can subtract, multiply, and divide numbers.

```
>>> 4 - 2
2
>>> 2 * 3
6
>>> 4 / 2
2.0
>>> 0.5 / 2
0.25
```

Note that division between two integers in Python 3 returns a float.

```
>>> 3 / 2
1.5
```

If you want your integers to round-down you can use a double slash:

```
>>> 3 // 2
1
```

We can use double asterisks to raise a number to a power. For example, 2 to the 10th power is 1024:

```
>>> 2 ** 10
1024
```

# Your Turn: REPL 🏁¶

## REPL Exercises¶

Let’s play around in the REPL. Open a command/terminal window and type `python3.6`

.

### Addition and Subtraction¶

- Add a few numbers, subtract a few numbers, and just get the feel of the REPL.
- What happens if you throw spaces in between the numbers? What happens if you don’t?
- What about parentheses?

### Multiplication, Division and Powers¶

- Play around with multiplication and division. Try big numbers, small numbers, and floats. Is anything surprising?
- What do you expect to happen if you raise a large number to the power of a large number? What did happen?
- Can you figure out what
`%`

does?

### Bonus: Text¶

- What if we just want to print text in the REPL? Can you figure out how to do that?