Paul Rudin wrote: > "Diez B. Roggisch" <de...@nospam.web.de> writes: > >> enzo michelangeli schrieb: >>> Let's suppose I want to create a list of n functions of a single >>> argument, returning the sum between argument and index in the list, so >>> that e.g.: >>> >>> f[0](10) will return 10 >>> f[3](12) will return 15 >>> >>> ...and so on. I had naively though of coding: >>> >>> f = [lambda x: x+j for j in range(n)] >>> >>> Unfortunately, each function in the list f[]() behaves as a closure, >>> and f[k](p) does NOT return p+k but p+j (for whatever value j has at >>> the moment: typically n, the last value assumed by j in the list >>> comprehension loop). >>> >>> Is there a way of achieving my goal? (Of course, n is not a constant >>> known in advance, so I can't manually unroll the loop.) >> >> You need to capture n into the closure of the lambda: >> >> f = [lambda x, n=n: x+j for j in xrange(n)] >> > > But be careful using such a technique with mutable arguments...
What makes "this technique" more susceptible to mutable argument issues than any other function or method-definition? Diez -- http://mail.python.org/mailman/listinfo/python-list
