type conversion problem

[kdt]

hi all,

I've just started back up with python after a looong break - it's great to be back :D

Anyway, I'm going through "how to think like a computer scientist" as a refresher and trying to come up with a function to return the sum of squares for a given number.

I decided to write it as a list comprehension:

sum(int(i)**2 for i in str(x))
 

I think I read somewhere that type conversion in python was costly? Is there a better way to do this?

Thanks

[bvdet]

hi all,

I've just started back up with python after a looong break - it's great to be back :D

Anyway, I'm going through "how to think like a computer scientist" as a refresher and trying to come up with a function to return the sum of squares for a given number.

I decided to write it as a list comprehension:

sum(int(i)**2 for i in str(x))
 

I think I read somewhere that type conversion in python was costly? Is there a better way to do this?

Thanks

I don't understand how you could sum the squares of a number. You can sum the squares of 2 numbers though. Why do you need to convert anything? What is 'x'?

>>> def sum_squares(x,y):
...     return sum([num**2 for num in [x,y]])
... 
>>> sum_squares(3,4)
25

Why go to all the trouble of a list comprehension or generator?

>>> def sum_squares(x,y):
...     return x**2+y**2
... 
>>> sum_squares(5,6)
61
>>> 

[kdt]

thanks for the reply

I'm summing the squares of elements in a list

x=[1, 2, 3]
 
# I would expect 14 as a result
 

cheers

[jlm699]

>>> x = [1,2,3]
>>> sum( [ i**2 for i in x ] )
14
>>> 
 

Why the type conversion?

[kdt]

>>> x = [1,2,3]
>>> sum( [ i**2 for i in x ] )
14
>>> 
 

Why the type conversion?

sorry I gave the wrong info

x=1234

[bvdet]

This is kind of screwy. Here's a couple of ways. One uses no conversion and the other converts once.

def sum_squares_int(num):
    num_list = []
    while num > 0:
        num_list.append(num%10)
        num /= 10
    return sum([i**2 for i in num_list])
 
def sum_squares_int1(num):
    return sum([(num/10**i%10)**2 for i in range(len(str(num)))])