def parse_row(input_row, parsers):
    """given a list of parsers (some of which may be None)
    apply the appropriate one to each element of the input_row"""
    return [parser(value) if parser is not None else value
            for value, parser in zip(input_row, parsers)]

def parse_rows_with(reader, parsers):
    """wrap a reader to apply the parsers to each of its rows"""
    for row in reader:
        yield parse_row(row, parsers)

def try_or_none(f):
    """wraps f to return None if f raises an exception
    assumes f takes only one input"""
    def f_or_none(x):   # <--- Function return THIS address
        try: 
            return f(x) # <--- Python MUST retain some state containing the input param
        except: 
            return None

    return f_or_none