What's wrong with the function

[RMartins]

does anybody knows why this function doesn´t work very well:

f=lambda n: reduce(lambda x,y:x**2+y**2, map(int,str(n)))

I want that this function add the square of the digits of a number

an example of what i want:

f(442)=4**2+4**2+2**2=36 and it's giving me f(442)=1028!!!:S

However fou numbers with 2 digits the function works!

[jrcagle]

First, the newer Python constructions pretty much eliminate the need for "map()".

Try this:

squaredigits = lambda x: sum([int(i)*int(i) for i in x])

Jeff

[bumsfeld]

Jeff's suggestion is modern Python. Make sure that your number is iterated as string:

squaredigits = lambda x: sum([int(i)*int(i) for i in str(x)])

print squaredigits(442)  # -->  36

Note: filter(), map() and reduce() will go away with Python30

# add this to future code
try: filter and map and reduce
except:
    def filter(f, s): return [x for x in s if f(s)]
    def map(f, *s): return [f(*x) for x in zip(*s)]
    def reduce(f, s, i=None):
        r = i
        for x in s:
            r = f(r, x)
        return r

Part of the reason is that list comprehensions are simply so much faster than using defined function call. Also reduce() isn't used much. Good news is that lambda will stay.

[RMartins]

Thanks it works!:)

[Ene Uran]

Hey Henri, thanks for the info on Python30.