Question

g = lambda x:[lambda x:x*1, lambda x:x*x, lambda x:x*x*x, lambda x:42][x%4](x)

[g(x) for x in xrange(12)]

What is the next value of this sequence?

Answer 1

Did you try it?

>>> g = lambda x:[lambda x:x*1, lambda x:x*x, lambda x:x*x*x, lambda x:42][x%4](x)
>>> [g(x) for x in xrange(12)]
[0, 1, 8, 42, 4, 25, 216, 42, 8, 81, 1000, 42]

Here is how each value is calculated:

[
 0,     # x is 0, x%4 is 0, so g(x) becomes (lambda x:x*1)(0) or 0*1
 1,     # x is 1, x%4 is 1, so g(x) becomes (lambda x:x*x)(1) or 1*1
 8,     # x is 2, x%4 is 2, so g(x) becomes (lambda x:x*x*x)(2) or 2*2*2
 42,    # x is 3, x%4 is 3, so g(x) becomes (lambda x:42)(3) or 42
 4,     # x is 4, x%4 is 0, so g(x) becomes (lambda x:x*1)(4) or 4*1
 25,    # x is 5, x%4 is 1, so g(x) becomes (lambda x:x*x)(5) or 5*5
 216,   # x is 6, x%4 is 2, so g(x) becomes (lambda x:x*x*x)(6) or 6*6*6
 42,    # x is 7, x%4 is 3, so g(x) becomes (lambda x:42)(7) or 42
 8,     # x is 8, x%4 is 0, so g(x) becomes (lambda x:x*1)(8) or 8*1
 81,    # x is 9, x%4 is 1, so g(x) becomes (lambda x:x*x)(9) or 9*9
 1000,  # x is 10, x%4 is 2, so g(x) becomes (lambda x:x*x*x)(10) or 10*10*10
 42     # x is 11, x%4 is 3, so g(x) becomes (lambda x:42)(11) or 42
]

Basically g(x) calls one of the functions in the list with x as the argument, when called in a list comprehension with xrange it will cycle through the functions, with every fourth call being the same function.

I know that this is just an exercise to aid in understanding Python, but you should note that this is horribly inefficient code, as all four functions are recreated on each call to g(). If you actually needed this behavior it would be better to just create a function with def that contains several if statements (which would make the code much more readable as well).