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Question

我想用map函数做一个有两个列表的字典。但似乎有些不对劲。你知道吗

我知道已经有zip和dict来做这项工作，但我想知道为什么这个代码出错了，在哪里。你知道吗

country = ['India', 'Pakistan', 'Nepal', 'Bhutan', 'China', 'Bangladesh']
capital = ['New Delhi', 'Islamabad','Kathmandu', 'Thimphu', 'Beijing', 
'Dhaka']

country_capital={}

def mydict(x,y):
  country_capital[x]=y
  return country_capital
national_info=map(mydict,country,capital)
print (list(national_info))

为什么打印如下：

[{'India': 'New Delhi', 'Pakistan': 'Islamabad', 'Nepal': 'Kathmandu', 'Bhutan': 'Thimphu', 'China': 'Beijing', 'Bangladesh': 'Dhaka'}, {'India': 'New Delhi', 'Pakistan': 'Islamabad', 'Nepal': 'Kathmandu', 'Bhutan': 'Thimphu', 'China': 'Beijing', 'Bangladesh': 'Dhaka'}, {'India': 'New Delhi', 'Pakistan': 'Islamabad', 'Nepal': 'Kathmandu', 'Bhutan': 'Thimphu', 'China': 'Beijing', 'Bangladesh': 'Dhaka'}, {'India': 'New Delhi', 'Pakistan': 'Islamabad', 'Nepal': 'Kathmandu', 'Bhutan': 'Thimphu', 'China': 'Beijing', 'Bangladesh': 'Dhaka'}, {'India': 'New Delhi', 'Pakistan': 'Islamabad', 'Nepal': 'Kathmandu', 'Bhutan': 'Thimphu', 'China': 'Beijing', 'Bangladesh': 'Dhaka'}, {'India': 'New Delhi', 'Pakistan': 'Islamabad', 'Nepal': 'Kathmandu', 'Bhutan': 'Thimphu', 'China': 'Beijing', 'Bangladesh': 'Dhaka'}]

我想要这样：

[{'India': 'New Delhi', 'Pakistan': 'Islamabad', 'Nepal': 'Kathmandu', 'Bhutan': 'Thimphu', 'China': 'Beijing', 'Bangladesh': 'Dhaka'}]

Answer 1

这里的人建议用更干净的方法来解决你的问题（你在问题中提到的一种方法）。你知道吗

关于你的问题：

why it prints as below:

[{'India': 'New Delhi', 'Pakistan': 'Islamabad', 'Nepal': 'Kathmandu', 'Bhutan': 'Thimphu', 'China': 'Beijing', 'Bangladesh': 'Dhaka'}, {'India': 'New Delhi', 'Pakistan': 'Islamabad', 'Nepal': 'Kathmandu', 'Bhutan': 'Thimphu', 'China': 'Beijing', 'Bangladesh': 'Dhaka'}, {'India': 'New Delhi', 'Pakistan': 'Islamabad', 'Nepal': 'Kathmandu', 'Bhutan': 'Thimphu', 'China': 'Beijing', 'Bangladesh': 'Dhaka'}, {'India': 'New Delhi', 'Pakistan': 'Islamabad', 'Nepal': 'Kathmandu', 'Bhutan': 'Thimphu', 'China': 'Beijing', 'Bangladesh': 'Dhaka'}, {'India': 'New Delhi', 'Pakistan': 'Islamabad', 'Nepal': 'Kathmandu', 'Bhutan': 'Thimphu', 'China': 'Beijing', 'Bangladesh': 'Dhaka'}, {'India': 'New Delhi', 'Pakistan': 'Islamabad', 'Nepal': 'Kathmandu', 'Bhutan': 'Thimphu', 'China': 
'Beijing', 'Bangladesh': 'Dhaka'}]

map方法将函数应用于列表的每个元素，并将返回值收集到新列表中。你知道吗

函数返回全局变量country_capital，您可以向该变量添加元素。因此，map（national_info）的输出是一个带有n指向country_capital指针的列表。你知道吗

如果您打印country_capital而不是national_info，您将得到所需的输出。你知道吗

Answer 2

您可以map()元组(country, capital)，然后包装dict以获得最终字典：

>>> country = ['India', 'Pakistan', 'Nepal', 'Bhutan', 'China', 'Bangladesh']
>>> capital = ['New Delhi', 'Islamabad','Kathmandu', 'Thimphu', 'Beijing', 'Dhaka']
>>> dict(map(lambda x, y: (x, y), country, capital))
  {'India': 'New Delhi', 'Pakistan': 'Islamabad', 'Nepal': 'Kathmandu', 'Bhutan': 'Thimphu', 'China': 'Beijing', 'Bangladesh': 'Dhaka'}

Answer 3

dict接受一个由两个元素iterable组成的iterable，所以您只需要发出

country_capital = dict(zip(country, capital))

（由于某些原因，您的预期结果将此字典包装在一个元素列表中。我看不出有什么理由这么做。）