I want to convert all the fields of str.split() at once...

field_converter.py

# -*- encoding: utf-8 -*-
def map_apply(proc, args):
    # return [f(x) for f, x in zip(proc, args)]
    return map(lambda f,x:f(x), proc, args)  # map(apply, proc, args) doesn't work like this

class FieldConverter:
    def __init__(self, *args):
        self._converters = args
        def conv_proc(f):
            def _wrap(conv_proc_to_num):
                def proc(x):
                    try:
                        return conv_proc_to_num(x)
                    except ValueError:
                        return 0
                return proc
            if f is None:
                return lambda s:s  # identity
            elif isinstance(f, str):
                return lambda s:s.decode(f)  # -> unicode
            elif f in (int, float):
                return _wrap(f)
            else:
                return f
        if len(args) > 0:
            self.converters = [conv_proc(f) for f in self._converters]
        else:
            self.converters = None

    def convert(self, fields):
        if self.converters:
            return map_apply(self.converters, fields)
        else:
            return fields

def split_and_convert(line, types, delim=' '):
    field_converter = FieldConverter(*types)
    return field_converter.convert(line.split(delim))


def test_map_apply():
    assert [0, -1, 3.14, 5.0] == map_apply([int,int,float,float], ['0','-1','3.14','5'])
    assert [0,u'日本語','日本語'] == map_apply([int,lambda s:s.decode('utf-8'),lambda s:s], ['0','日本語','日本語'])

def test_field_converter():
    assert [0, -1, 3.14, 5.0] == FieldConverter(int,int,float,float).convert(['0','-1','3.14','5'])
    assert [0,u'日本語','日本語'] == FieldConverter(int,'utf-8',None).convert(['0','日本語','日本語'])

def test_split_and_convert():
    assert [0, -1, 3.14, 5.0] == split_and_convert('0\t-1\t3.14\t5', (int,int,float,float), '\t')
    assert [0, u'日本語', '日本語'] == split_and_convert('0,日本語,日本語', (int,'utf-8',None), ',')