将 ._replace 的命名元组字段名称作为函数的参数传递

Question

所以我有一个命名的元组，比如：

from collections import namedtuple

Symbol = namedtuple('Symbol', 'name code industry date_au open high low close volume weekday_au date_utc_unixtimestamp prev_volume', defaults = ('DEFAULT', 'DEF', 'DEFAULT', '01/01/1970', 0.0, 0.0, 0.0, 0.0, 0, 'Mon', 0, 0))

我做了一些测试数据：

ont_data = [
Symbol(name = '1300 SMILES LIMITED', code ='ONT', industry = 'Tech', date_au = '03/05/2020', open = 10.0, high = 12.0, low = 9.5, close = 11.0, volume = 1000, weekday_au = 'Sun', date_utc_unixtimestamp = 123),
Symbol(name = '1300 SMILES LIMITED', code ='ONT', industry = 'Tech', date_au = '15/05/2020', open = 12.0, high = 12.0, low = 5.5, close = 9.0, volume = 999, weekday_au = 'Fri', date_utc_unixtimestamp = 125),
Symbol(name = '1300 SMILES LIMITED', code ='ONT', industry = 'Tech', date_au = '17/01/2020', open = 4.0, high = 90.0, low = 54.5, close = 74.0, volume = 27, weekday_au = 'Wed', date_utc_unixtimestamp = 5)
]

现在我想创建这个命名元组的副本，并对特定属性进行一些动态替换：

def set_prev_val(symbol, prev_values, field_to_update):
    """
    Iterate over a copy of Symbol named tuple and replace some attribute values.

    Return a copy of Symbol named tuple with replaced previous values of some field_to_update

    args:
      @symbol - A descending sorted named tuple representing stock symbol data
      @prev_values - A list of previous values (from a descending sorted Symbol)
      @field_to_update - A field in a Symbol named tuple to update
   """
    symbol_copy = symbol

    for row in range(0, len(symbol_copy)):
        symbol_copy[row] = symbol[row]._replace(field_to_update = prev_values[row])
    return symbol_copy

当我用 prev_values_data = [1,2,3] 测试这个时，我得到：

ValueError: Got unexpected field names: ['field_to_update']

我想要的是用 prev_values_data

的值更新 prev_volume 字段

我认为不是传递 field_to_update 的字符串值，而是将命名元组中属性的实际名称作为参数名称！！！

有没有办法让我能够将一些 'name' 属性作为参数从函数传递到命名元组中的 ._replace 调用？（假设 name 存在于命名的元组属性名称中）

Python 3.7

Answer 1

创建一个匿名 dict 并解压它：

symbol_copy[row] = symbol[row]._replace(**{field_to_update: prev_values[row]})

通过field_to_update=prev_values[row]传递的普通关键字参数是静态的；它将左侧作为固定字符串传递，而不是变量（它甚至不允许引用它）。但是 dict 文字语法需要引用字符串键，因此它将 field_to_update 视为变量，正如预期的那样。

将 ._replace 的命名元组字段名称作为函数的参数传递

Passing named tuple field name for a ._replace as an argument from a function

python

python-3.x

namedtuple