如何在数据类型定义中没有uuu len_uuuu的情况下将uuu len_uuu添加到对象中?

根据文件,这不起作用,因为:

>>> class C:
...     pass
...
>>> c = C()
>>> c.__len__ = lambda: 5
>>> len(c)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: object of type 'C' has no len()

https://docs.python.org/3/reference/datamodel.html#special-method-lookup

我在一个函数生成器上试过这个,它没有 __len__ ,但我事先知道它的长度,然后,我试着用类似于 c.__len__ = lambda: 5 ,但它一直说生成器对象没有长度。

def get_sections(loaded_config_file):
    for module_file, config_parser in loaded_config_file.items():
        for section in config_parser.sections():
            yield section, module_file, config_parser

我将生成器(没有长度)传递给另一个函数(还有另一个生成器),它通过调用 len() :

def sequence_timer(sequence, info_frequency=0):
    i = 0
    start = time.time()
    if_counter = start
    length = len(sequence)
    for elem in sequence:
        now = time.time()
        if now - if_counter < info_frequency:
            yield elem, None
        else:
            pi = ProgressInfo(now - start, float(i)/length)
            if_counter += info_frequency
            yield elem, pi
        i += 1

https://github.com/arp2600/Etc/blob/60c5af803faecb2d14b5dd3041254ef00a5a79a9/etc.py

然后,当尝试添加 __莱恩__ 把某事归因于某人 get_sections ,因此出现错误:

get_sections.__len__ = lambda: calculated_length
for stuff, progress in sequence_timer( get_sections ):
    section, module_file, config_parser = stuff

TypeError: object of type 'function' has no len()