python - OrderedDict 仅打算更新一个键值对时更新所有键值对

Question

我有一个 python OrderedDict，当我只更新一个键值时，所有其他键值对也会更新。我已经包含了下面的源代码和跟踪。

我期望有一个 key 对 (2014, {'start': 2014, 'end': 2015})，但这里的情况并非如此。

import datetime
import collections
import math
from decimal import Decimal
from dateutil.relativedelta import relativedelta



def get_ordered_dict(start, end, intial_value):
    d = collections.OrderedDict()
    for i in range(start, end+1):
        d[i] = intial_value
    return d


start_year = 2014
end_year = start_year + 39 + 1
od = get_ordered_dict(start_year, end_year, {} )

for year in od.keys():
    print year
    d = od[year]
    d['start'] = year
    d['end'] = year + 1
    print od

返回:

OrderedDict([(2014, {'end': 2053, 'start': 2052}),
             (2015, {'end': 2053, 'start': 2052}),
             (2016, {'end': 2053, 'start': 2052}),
             (2017, {'end': 2053, 'start': 2052}),
             (2018, {'end': 2053, 'start': 2052}),
             (2019, {'end': 2053, 'start': 2052}),
             (2020, {'end': 2053, 'start': 2052}),
             (2021, {'end': 2053, 'start': 2052}),
             (2022, {'end': 2053, 'start': 2052}),
             (2023, {'end': 2053, 'start': 2052}),
             (2024, {'end': 2053, 'start': 2052}),
             (2025, {'end': 2053, 'start': 2052}),
             (2026, {'end': 2053, 'start': 2052}),
             (2027, {'end': 2053, 'start': 2052}),
             (2028, {'end': 2053, 'start': 2052}),
             (2029, {'end': 2053, 'start': 2052}),
             (2030, {'end': 2053, 'start': 2052}),
             (2031, {'end': 2053, 'start': 2052}),
             (2032, {'end': 2053, 'start': 2052}),
             (2033, {'end': 2053, 'start': 2052}),
             (2034, {'end': 2053, 'start': 2052}),
             (2035, {'end': 2053, 'start': 2052}),
             (2036, {'end': 2053, 'start': 2052}),
             (2037, {'end': 2053, 'start': 2052}),
             (2038, {'end': 2053, 'start': 2052}),
             (2039, {'end': 2053, 'start': 2052}),
             (2040, {'end': 2053, 'start': 2052}),
             (2041, {'end': 2053, 'start': 2052}),
             (2042, {'end': 2053, 'start': 2052})])

Answer 1

在

def get_ordered_dict(start, end, intial_value):
    d = collections.OrderedDict()
    for i in range(start, end+1):
        d[i] = intial_value
    return d

您为每个 d[i] 分配对相同 initial_value 的引用，在本例中是相同的字典

od = get_ordered_dict(start_year, end_year, {})

因此，在循环中，您会一遍又一遍地修改同一个字典。

分配唯一字典引用的一种方法是制作initial_value的(浅)副本:

d[i] = intial_value.copy()  # [sic]

您还可以将 initial_value 设置为默认为 None 的关键字参数:

def get_ordered_dict(start, end, intial_value=None):
    ...
        # assuming intial_value will always be a dict
        d[i] = intial_value.copy() if intial_value is not None else {}