Though a lot of stealing goes on between language designers, they often regret it later. Matz wished he never stole Perl's "ugly" $ sigils for Ruby, while in Larry Wall: Perl vs Python 11th State of the Onion Larry regrets stealing Python's object model:

I don't really know much about Python. I only stole its object system for Perl 5. I have since repented.

Why has Larry repented? A clue may be given in Slashdot interview with Larry Wall:

But I think the success of Python has mostly to do with being light enough in its OO model that it could move into some ecological niches more quickly than the Perl 5 design could. Perl has always considered itself primarily a programmer-centric language, while Python has always considered itself to be more institution-centric. So in a sense it's a bit dumbed down, much like Java. You'll note both of those languages make their greatest appeal to managers ... If Python's object model matches how you want to do things, it's fine for that. If it's not, Python doesn't really provide a coherent meta-object model underneath, just a lot of hooks, which might or might not give you the flexibility you need ...

Other quotes from Larry Wall: Perl vs Python 11th State of the Onion:

a great deal of Ruby's syntax is borrowed from Perl, layered over Smalltalk semantics. I've always viewed Ruby as a much closer competitor for Perls ecological niche, not just because of the borrowed ideas, but because both Perl and Ruby take their functional programming support rather more seriously that Python does.

Other quotes from Slashdot interview with Larry Wall:

Some Pythonistas claim that Python is a good functional programming language, mostly on the strength of list comprehensions, but in my estimation Python has only half-hearted FP support; it really doesn't provide the benefits of lexical scoping, closures, laziness, or higher-order programming that I'd expect in a strong FP contender, nor does it encourage you to think that way ... If you want concurrency with a global interpreter lock, Python might suit. But if you want a concurrency model designed to scale to multicore/manycore, look to Perl 6, which avoids global bottlenecks and non-composable primitives, but instead borrows composable ideas from Haskell, Go, Erlang, and C# instead.