> Right idea: now to remove all those intermediate lists you construct. > 1. reversed(val) creates an iterator that runs over the elements (here > of a string) in reverse order. > 2. enumerate() is usually better than using an explicit list index. > 3. You can use a generator in your sum to avoid constructing the final > list. > > Applying these to your function, and noting that n << k is nicer than > n * 2 ** k, we get a one-liner: > > def bin2dec(val): > return sum(int(i) << k for k, i in enumerate(reversed(val))) > > Or a slightly nicer alternative is to filter the generator using 'if': > > def bin2dec(val): > return sum(1 << k for k, i in enumerate(reversed(val)) if int(i)) > > -- > Paul Hankin
Thank you for this reply, I only wish I could come up with functions so elegantly refined! I know '<<' is shifting x over by n bits; but could you point me to some literature that would explain why it is the same as "x*2**n"? (Googling only returns bit shift, but doesn't necessarily explain the manner in which you are using it) I will have to read up more on Generators, but maybe you can give me a lowdown on why sum([1 << k for k, i in enumerate(reversed(val)) if int(i)]) is less efficient than using a Generator (is the generator a 'temporary' list?) sum(1 << k for k, i in enumerate(reversed(val)) if int(i)) -- Parnell Springmeyer -- http://mail.python.org/mailman/listinfo/python-list
