Python in a Nutshell, 2nd Edition

Universal Functions (ufuncs)

Numeric supplies named functions with the same semantics as Python’s arithmetic, comparison, and bitwise operators, and mathematical functions like those supplied by built-in modules math and cmath (covered in The math and cmath Modules), such as sin, cos, log, and exp.

These functions are objects of type ufunc (which stands for “universal function”) and share several traits in addition to those they have in common with array operators (element-wise operation, broadcasting, coercion). Every ufunc instance u is callable, is applicable to sequences as well as to arrays, and accepts an optional output argument. If u is binary (i.e., if u accepts two operand arguments), u also has four callable attributes, named u.accumulate, u.outer, u.reduce, and u.reduceat. The ufunc objects supplied by Numeric apply only to arrays with numeric typecodes (i.e., not to arrays with typecode 'O' or 'c') and Python sequences of numbers.

When you start with a list L, it’s faster to call u directly on L rather than to convert L to an array. u’s return value is an array a; you can perform further computation, if any, on a; if you need a list result, convert the resulting array to a list at the end by calling method tolist. For example, say you must compute the logarithm of each item of a list and return another list. On my laptop, with N set to 2222, a list comprehension such as:

def logsupto(N):
    return [math.log(x) for x in range(2,N)]

takes about 5.2 milliseconds. Using Python’s ...