Can a lambda function call itself recursively in Python?

The only way I can think of to do this amounts to giving the function a name: fact = lambda x: 1 if x == 0 else x * fact(x-1) or alternately, for earlier versions of python: fact = lambda x: x == 0 and 1 or x * fact(x-1) Update : using the ideas from the other answers, I was able to wedge the factorial function into a single unnamed lambda: map(lambda n: (lambda f, *a: f(f, *a))(lambda rec, n: 1 if n == 0 else n*rec(rec, n-1), n), range(10)) 1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880 So it's possible, but not really recommended!

The only way I can think of to do this amounts to giving the function a name: fact = lambda x: 1 if x == 0 else x * fact(x-1) or alternately, for earlier versions of python: fact = lambda x: x == 0 and 1 or x * fact(x-1) Update: using the ideas from the other answers, I was able to wedge the factorial function into a single unnamed lambda: >>> map(lambda n: (lambda f, *a: f(f, *a))(lambda rec, n: 1 if n == 0 else n*rec(rec, n-1), n), range(10)) 1, 1, 2, 6, 24, 120, 720, 5040, 40320, 362880 So it's possible, but not really recommended!

1 map(lambda n: (lambda f, n: f(f, n))(lambda f, n: n*f(f, n-1) if n > 0 else 1, n), range(10)) – J.F. Sebastian Jan 27 '09 at 12:39 Useless and fun. That's why I love computing. – Kevin Samuel Nov 18 '09 at 13:23 FWIW, here's how to generate numbers in the Fibonacci series with the same technique (assigning it a name): fibonacci = lambda n: 0 if n == 0 else 1 if n == 1 else fibonacci(n-1)+fibonacci(n-2) .

– martineau Nov 1 '10 at 19:52.

You can't directly do it, because it has no name. But with a helper function like the Y-combinator Lemmy pointed to, you can create recursion by passing the function as a parameter to itself (as strange as that sounds): # helper function def recursive(f, *p, **kw): return f(f, *p, **kw) def fib(n): # The rec parameter will be the lambda function itself return recursive((lambda rec, n: rec(rec, n-1) + rec(rec, n-2) if n>1 else 1), n) # using map since we already started to do black functional programming magic print map(fib, range(10)) This prints the first ten Fibonacci numbers: 1, 1, 2, 3, 5, 8, 13, 21, 34, 55.

I think I finally understand what the Y combinator is for. But I think that in Python it would generally be easier to just use "def" and give the function a name... – pdc Jan 28 '09 at 13:59 Funny thing is, your Fibonacci example is a great example of something more naturally done with a generator. :-) – pdc Jan 28 '09 at 13:59 A much better answer than "No".

– new123456 Jul 28 at 22:19.

I have never used Python, but this is probably what you are looking for.

Yes. I have two ways to do it, and one was already covered. This is my preferred way.(lambda v: (lambda n: n * __import__('types').

FunctionType( __import__('inspect').stack()00. F_code, dict(__import__=__import__, dict=dict) )(n - 1) if n > 1 else 1)(v))(5).

1 I don't know Python, but that looks terrible. There's really got to be a better way. – Kyle Cronin Jan 27 '09 at 3:41 You have to learn to appreciate obsfucated code, man.

:( – Aaron Gallagher Jan 27 '09 at 4:56 +1 for teaching me a new way to abuse Python. – Deestan Jan 27 '09 at 10:14 nobody - the point is that this looks horrible for a reason. Python isn't designed for it, and it's bad practice (in Python).

Lambdas are limited by design. – Gregg Lind Jan 27 '09 at 22:11 4 Yeah, +1 for the worst Python code ever. When Perl people say "You can write maintainable code in Perl if you know what you are doing", I say "Yeah, and you can write unmaintainable code in Python if you know what you are doing".

:-) – Lennart Regebro Jan 27 '097 at 22:11.

If you were truly masochistic, you might be able to do it using C extensions, but to echo Greg (hi Greg! ), this exceeds the capability of a lambda (unnamed, anonymous) functon. No.(for most values of no).

I cant really gove you an answer,but what I can give you is a way to a solution, that is you have to find the anglde that you relate to or peaks your interest. A good paper is one that people get drawn into because it reaches them ln some way.As for me WW11 to me, I think of the holocaust and the effect it had on the survivors, their families and those who stood by and did nothing until it was too late.