My favorite editor for writing any scripting language, not just Python but Ruby, perl, etc… is Textmate. Since I do this for a living I am still using TextMate version 1 that I paid for ages ago. Textmate version 2 is now open source software and as such is free to download and even change. Both versions can be downloaded from the Macromates Download page.
I prefer Textmate to BBEdit for writing in scripting languages because BBEdit doesn't allow editing while it is running a script. For all of my other text editing needs I prefer BBEdit and it is set as my system default for most types of text files. Every Mac I have owned has had a copy of BBEdit, since about 1989.
If you want to get a taste of what BBEdit is like, your friend can try BBEdit's little brother, TextWrangler. This works the same way, and for scripting languages, has the same shortcomings as BBEdit. TextWrangler is available on the Mac App Store for free.