Fredrik Johansson <[EMAIL PROTECTED]> added the comment: Some elaboration (that perhaps could be adapted into the documentation or at least source comments).
There are two primary uses for numbits, both of which justify (0).numbits() == 0. The first is that for positive k, n = k.numbits() gives the minimum width of a register that can hold k, where a register can hold the 2**n integers 0, 1, ..., 2**n-1 (inclusive). This definition continues to make sense for k = 0, n = 0 (the empty register holds the 2**0 = 1 values 0). In Python terms, one could say that self.numbits() "returns the smallest n such that abs(self) is in range(2**n)". Perhaps this would make a clearer docstring? Second, k.numbits() (plus/minus 1, or perhaps multiplied by a constant factor) measures the number of steps required to solve a problem of size k using various divide-and-conquer algorithms. The problem of size k = 0 is trivial and therefore requires (0).numbits() == 0 steps. In particular, if L is a sorted list, then len(L).numbits() exactly gives the maximum number of comparisons required to find an insertion point in L using binary search. Finally, the convention (-k).numbits() == k.numbits() is useful in contexts where the number k itself is the input to a mathematical function. For example, in a function for multiplying two integers, one might want to choose a different algorithm depending on the sizes of the inputs, and this choice is likely to be independent of signs (if not, one probably needs to check signs anyway.) _______________________________________ Python tracker <[EMAIL PROTECTED]> <http://bugs.python.org/issue3439> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: http://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
