Python in a Nutshell

Name

reduce

Synopsis

reduce(func,seq[,init])

Applies funct to the items of seq, from left to right, to reduce the sequence to a single value. func must be callable with two arguments. reduce calls func on the first two items of seq, then on the result of the first call and the third item, and so on. reduce returns the result of the last such call. When init is present, it is used before seq’s first item, if any. When init is missing, seq must be non-empty. When init is missing and seq has only one item, reduce returns seq [0]. Similarly, when init is present and seq is empty, reduce returns init. The built-in reduce is equivalent to:

def reduce_equivalent(func,seq,init=None):
    if init is None: init, seq = seq[0], seq[1:]
    for item in seq: init = func(init,item)
    return init

A typical use of reduce is to compute the sum of a sequence of numbers:

thesum = reduce(operator.add, seq, 0)