Python字典中的更新方法
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Update method in Python dictionary
提问by Max Kim
I was trying to update values in my dictionary, I came across 2 ways to do so:
我试图更新字典中的值，我遇到了两种方法：
product.update(map(key, value))
product.update(key, value)
What is the difference between them?
它们之间有什么区别？
采纳答案by Martijn Pieters
The difference is that the second method does not work:
不同之处在于第二种方法不起作用：
>>> {}.update(1, 2)
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
TypeError: update expected at most 1 arguments, got 2
dict.update()expects to find a iterable of key-value pairs, keyword arguments, or another dictionary:
dict.update()期望找到一个可迭代的键值对、关键字参数或另一个字典：
Update the dictionary with the key/value pairs from other, overwriting existing keys. Return
None.
update()accepts either another dictionary object or an iterable of key/value pairs (as tuples or other iterables of length two). If keyword arguments are specified, the dictionary is then updated with those key/value pairs:d.update(red=1, blue=2).
使用其他键/值对更新字典，覆盖现有键。返回
None。
update()接受另一个字典对象或键/值对的可迭代对象（作为元组或其他长度为 2 的可迭代对象）。如果指定关键字参数，字典，然后用这些键/值对更新：d.update(red=1, blue=2)。
map()is a built-in method that produces a sequence by applying the elements of the second (and subsequent) arguments to the first argument, which must be a callable. Unless your keyobject is a callable and the valueobject is a sequence, your first method will fail too.
map()是一个内置方法，它通过将第二个（和后续）参数的元素应用于第一个参数来生成一个序列，第一个参数必须是可调用的。除非您的key对象是一个可调用value对象并且该对象是一个序列，否则您的第一个方法也会失败。
Demo of a working map()application:
一个工作map()应用程序的演示：
>>> def key(v):
... return (v, v)
...
>>> value = range(3)
>>> map(key, value)
[(0, 0), (1, 1), (2, 2)]
>>> product = {}
>>> product.update(map(key, value))
>>> product
{0: 0, 1: 1, 2: 2}
Here map()just produces key-value pairs, which satisfies the dict.update()expectations.
这里map()只生成键值对，满足dict.update()预期。
