Python dictionary setdefault method and the get method

在pythonin the dictionary object,You can use the key name to get the key value directly,像這樣：

>>> d = {
"x":1,"y":2}
>>> d["x"]
1
>>> d["y"]
2
>>>

But if the key name does not exist,則會報錯：

>>> d["z"]
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
KeyError: 'z'
>>>

This affects the executable of the code.不過可以使用get方法或者setdefaultmethod to avoid this error,The role of both methods is to get the key value of the key,如果鍵存在於字典中,則返回鍵值;If the key does not exist in the dictionary,則返回一個默認值(這個值默認是None,But you can set it yourself),如下：

d = {
"x":1, "y":2}
print(d.get("z"))
print(d.get("z",9))

輸入結果如下：

None
9

可以看到,“z“This key does not exist in the dictionary,使用get方法獲取時,就返回了None,第二次使用get方法時,The default value returned is set 9 .setdefault方法也是一樣的.

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d = {
"x":1, "y":2}
print(d.setdefault("z"))
print(d.setdefault("z",9))