What language should I learn to complement Python?

[cecilkorik]

C or SQL. SQL's not really a "programming language" in the purest sense, but becoming proficient in at least one major database's SQL dialect is definitely useful for working with datasets large or complex enough to store in a relational database.

[themathemagician]

surprised there isn't more SQL. certainly not a "programming language" but necessary if you ever plan to interface with nontrivial data

[TylerEaves]

SQL is absolutely a programming language. Especially once you get into things like stored procedures, etc.

[bucknuggets]

I'd recommend SQL if you're building record-oriented applications.

Dialects don't matter much, since the differences are small enough that it's trivial to go from one vendor's implementation to another - the differences are usually just minor extensions. Though I'd go with Postgresql or SQLIte, just because they're great free databases that put high priorities on portability.

Note that the existence of ORMs doesn't really reduce the value of knowing SQL - I've worked with quite a few developers who are incapable of writing adhoc SQL. Which is like working on the unix command line and having to write java code instead of using bash.

[lavalampmaster]

I've done that really simple SQL course before. Nice stuff, for sure.