python - 根据输入标志返回不同变量的优雅方式

Question

我有一个函数可以打开一个文本文件，解析一堆数据并返回一个数组中的数字结果。现在，我还希望此函数能够即时执行一些可选计算，并在需要时返回这些值。

对于单个标志，这是相当干净的，例如:

def read_data(file_name, calc_a=False):
    # do normal parsing and store data in 'xyz'
    if calc_a:
        # calc some other stuff and store in 'a'
        return xyz, a
    else:
        return xyz

现在如果我想要多个可选标志，事情很快就会变得困惑，例如:

def read_data(file_name, calc_a=False, calc_b=False):
    # do normal parsing and store data in 'xyz'
    if calc_a:
        # calc some other stuff and store in 'a'
    if calc_b:
        # calc some other stuff and store in 'b'

    if calc_a and calc_b:
        return xyz, a, b
    elif calc_a:
        return xyz, a
    elif calc_b:
        return xyz, b
    else:
        return xyz

有没有更简洁的方法来处理这种情况？

Answer 1

def read_data(file_name, *extras):
    # Read the data from file_name, organizing in a dict,
    # using the key names that your caller will pass into the function.
    # In this example, we have the main data that will always be
    # returned, plus optional data stored under keys a, b, c, d.
    data = dict(_main = 'MAIN', a = 'AA', b = 'BB', c = 'CC', d = 'DD')

    # Return a tuple, list, or even dict of that data.
    ks = sorted(data.keys())
    return tuple(data[k] for k in ks if k in extras or k == '_main')

# Caller requests the optional data they want.
# This example shows the caller passing a list of optional data keys.
# You could also have them pass keyword args instead.
wanted = 'a b d'.split()
print read_data('data_file', *wanted)  # ('MAIN', 'AA', 'BB', 'DD')