I have been working with python for a couple of years now and I want to play with a new language. Colleagues suggested C but what would people recommend as the next step?

Go is fun.

Personally C is a very nice contrast to Python. I love working with both so my recommendation would be C as well

If you want a smooth transition from python to c than go with go

c++, beautiful powerfull and god dammit another error without description

Common Lisp could be the next step language-wise.

@ac1235 I was going to suggest either that or Clojure

Or go the full way with functional and do Haskell

@Hedgepig I would have recommended SML or Haskell if he would do functional programming, but he obviously is into imperative languages.

@ac1235 ah right, I didn't make that assumption, all he says is he wants to try a new language.

I'd recommend Rust, it's like C, but it learns you memory management without many of the hassles like double deallocation, dereferencing null pointers, …

IMO it is also has an easier build system, and a package mannager.

Some other features that rust hs in common with higher-level languages that you don't find in C: destructuring variables, most things are an expression, implicit return, and maybe the best: Unicode support.

You will fight the borrow checker at first and struggle with the functional nature of the language, but if you work yourself through the book you should be fine.

How about trying something completely different?
Like imperative languages
Such as Haskell?