python，如何通过改变其格式来更新字典？

Question

所以我想做的是改变字典 该函数有 4 个参数 格式为 {country_name:[location, population, president]}

def mutate dic(dic_format, country_name, field, new_data):
  dic_format = {country_name:['location', 'population', 'president']}
  if field == 'location':
    dic_format[:] = {country_name:[val, 'population', 'president']}
  elif field == 'population':
    dic_format[:] = {country_name:['location', val, 'president']}
  elif field == 'president':
    dic_format[:] = {country_name:['location', 'population', val]}

这就是我的想法，我知道这行不通。 我该怎么做才能得到这样的输出:

>>>dict = {'canada':['North_America', '100M+', 'none']}
>>>mutate_dic(dict, 'canada', 'population', '150M+')
>>>dict
{'canada':['North_America', '150M+', 'none']}

Answer 1

更好的数据结构将使这变得容易。例如，而不是这个:

{country_name: [location, population, president]}

…假设你有这个:

{country_name: 
 {'location': location, 'population': population, 'president': president}}

那么你的函数就是:

def mutate_dic(dic, country_name, field, new_data):
    dic[country_name][field] = new_data

虽然实际上，在这种情况下，函数只是混淆了事物。哪个更明显？

dic['canada']['population'] = '150M+'
mutate_dic(dic, 'canada', 'population', '150+')

---

例如，如果您有一个 Country 类，您可以做得更好——当有一个简短的静态字段列表时，为什么不直接将它们设为属性呢？

class Country(object):
    def __init__(self, location, population, president='none'):
        self.location = location
        self.population = population
        self.president = president

dic = {'canada': Country('North America', '150M+')}

dic['canada'].population = '100M+'

---

无论哪种方式，您都可以将数据文件直接读入其中一种格式。由于您没有向我们展示该文件，我将制作一个并展示如何阅读它:

数据文件:

name,location,population,president
Canada,North America,100M+,none
France,Europe,65.7M,Hollande

脚本:

import csv
with open('datafile', 'rb') as f:
    reader = csv.DictReader(f)
    dic = {row['name'].lower(): row for row in reader}
print dic

输出:

{'canada': {'location': 'North America',
  'name': 'Canada',
  'population': '100M+',
  'president': 'none'},
 'france': {'location': 'Europe',
  'name': 'France',
  'population': '65.7M',
  'president': 'Hollande'}}

---

但如果最坏的情况发生，您总是可以在输入后从一种格式转换为另一种格式:

dic = {name: {'location': value[0], 'population': value[1], 'president': value[2]}
       for name, value in dic.items()}

……或者……

dic = {name: Country(*value) for name, value in dic.items()}