cpx...@gmail.com wrote: >>>> li=[lambda :x for x in range(10)] >>>> res=li[0]() >>>> print res > 9 > > why?
Look what happens if you look up x manually: >>> li = [lambda :x for x in range(10)] >>> x 9 So at this point x is 9 and a function written to return the value bound to the name x will return 9 >>> li[0]() 9 >>> x = 42 >>> li[0]() 42 This is called late binding and neither the lambda behaves like any other function >>> def f(): return x ... >>> f() 42 >>> x = "whatever" >>> f() 'whatever' To get the desired results you can either use default values which are bound when the function is created >>> li = [lambda x=x: x for x in range(9)] >>> li[0]() 0 >>> li[5]() 5 or a closure: >>> li = [(lambda x: lambda: x)(x) for x in range(9)] >>> li[0]() 0 >>> li[5]() 5 This looks less messy when you use a function: >>> def make_const_func(value): ... return lambda: value ... >>> li = [make_const_func(x) for x in range(9)] >>> li[7]() 7 In both cases the value is bound inside a function and not affected by the current binding of the global x. In Python 3 the situation is almost the same, except that the x from the list comprehension is no longer exposed to the enclosing namespace. -- https://mail.python.org/mailman/listinfo/python-list
