pretty is as pretty does

[oldlady]

Please explain the meaning of this idiom. Thanks.

[Heba]

I think it means,
"outer beauty is nice but inner beauty is more important."
http://www.dennydavis.net/poemfiles/beauty.htm

[oldlady]

Does 'pretty does' function as a noun? What is it that 'pretty does'?
I'm at a loss.

[Rusty]

Does 'pretty does' function as a noun? What is it that 'pretty does'?
I'm at a loss. Yes, pretty acts as a noun. The meaning is: a pretty person is only as beautiful/pretty as her actions are beautiful/kind/generous, etc.

[oldlady]

So both pretties are nouns. Thank you Rusty.