On writing Python one-liners.

Abstraction: Using lambdas to encode any Python program as one line

Key points:

• Variable assignments can be eliminated by converting locals into function arguments passed to immediately-invoked lambdas
• Local function definitions are replaced with lambda arguments: (lambda g, h, n: g(h(g(h(n)))))(lambda n: 2n+1, lambda n: 3n-2, n)
• Recursion requires self-application: rewrite fact(n) as urfact(f, n) where f is passed as itself, enabling f(f, n-1)
• Lazy evaluation for conditionals is achieved by wrapping branches in zero-argument lambdas: {True: lambda: 1, False: lambda: n*f(f, n-1)}[n<=1]()
• The technique can theoretically compile any Python subset into a single expression, but the result is unmaintainable

Connections: Functional Programming · Lambda Calculus · Python Programming

Source: http://blog.sigfpe.com/2008/09/on-writing-python-one-liners.html