---
## Lesson Objectives
*After this lesson, you will be able to…*
- Write Python 3 scripts locally.
- Run Python 3 scripts via the command prompt.
---
## Defining Assumptions
We can't use repl.it forever! We can run Python right on our computers.
* GA uses Macs for its default curriculum.
* We are happy to help you program Python on Windows or Linux as well.
* Sometimes you may need to ask questions about subtle differences!
---
## In-Line REPL
Let's check out a REPL.
- `Read-Evaluate-Print-Loop`.
- An interactive way to code.
Let's do it!
* Open your terminal.
* Then, open your in-line REPL:
Mac/Linux:
```
python
```
Windows:
```
py
```
---
## We Do: Interactive Development
You can type any Python code you want here. Let's declare a variable and do some math:
```python
x = 4
y = 5
print(x + y)
```
> **Pro tip:** `exit()` is the command for when you want to get out of this environment!
---
## We Do: Local Files
We can create a file with a `.py` extension — we can execute properly written Python code in a `.py` file.
1. Create a new file with a `.py` extension. Let's call it `my_file.py`.
2. Open `my_file.py` in `Atom`.
3. In this file, declare some variables. Let's mix integers and strings!
```python
favorite_tv_show = "Ninja Warrior"
obstacles_cleared = 5
time = "3 min, 20 sec"
print("I cleared", obstacles_cleared, "on", favorite_tv_show, "in", time)
```
Save and close your file.
> **Pro tip:** Make sure you have a `print` statement.
---
## We Do: Running Local Files
Now we have code in a file, but we need to run it.
* Back on your terminal, we'll navigate to where that file is located:
* `cd` stands for "change directory" ("directory" is another word for "folder").
* `cd my_folder` changes to the directory `my_directory`.
* `cd ..` goes up to the parent folder of the one you're in.
* Running the file varies slightly between Windows and Mac/Linux:
* Mac/Linux: `python my_file.py`
* Windows: `py my_file.py`
Raise your hand if you need help!
---
## Summary
* We now have Python 3 — the latest and greatest — installed.
* We can use our in-line REPL in the terminal.
* We can execute a local `.py` file with Python code in it.
* We know how to do this regardless of whether we use Mac, Linux, or Windows.
> Any questions?
---
## Additional Resources
* [Linux Command Line Cheat Sheet](https://www.cheatography.com/davechild/cheat-sheets/linux-command-line/)
* [Mac Command Line Cheat Sheet](https://www.git-tower.com/blog/command-line-cheat-sheet/)
* [Windows Command Line Cheat Sheet](http://simplyadvanced.net/blog/cheat-sheet-for-windows-command-prompt/)