Tutorial on setdefault() method of dictionary in Python

When learning python dictionary operation methods, many students feel that the setdefault() method is more difficult to understand than other basic dictionary operation methods, so I thought of summarizing the following. The following article mainly introduces Python dictionaries to you. The setdefault() method, friends in need can refer to it, let’s take a look below.

Preface

As mentioned in the basic knowledge of Python, a dictionary is a variable data type, and its parameters are key pairs. The setdefault() method is similar to the dictionary's get() method in some places, and both can get the value corresponding to a given key. But the setdefault() method can set the corresponding value for a given key when the given key is not included in the dictionary.

The setdefault method prototype of Python dictionary is as follows:

dict.setdefault(key, default=None)

If the given key is in the dictionary, return the If the value is not in the dictionary, insert the key into the dictionary and set the value to the specified default parameter. The default value of default is None.

Using the setdefault method is equivalent to the following operation:

if key in dict:
 reurn dict[key]
else:
 dict[key] = default
 return default

This method is somewhat similar to the get method of the dictionary. But there are some differences. The dict.get and dict.setdefault methods can return the value when the key exists in the dictionary, and can also return the default value when the key is not in the dictionary. The difference between the two methods is that when the key is not in the dictionary, the setdefault method will insert the default key value into the dictionary and return it, while the get method only returns the default value and does not insert a new key into the dictionary.

Example:

>>> dct = {}
>>> dct
{}
>>> dct["name"] = "huoty"
>>> dct
{'name': 'huoty'}
>>> dct.setdefault("name", "esenich")
'huoty'
>>> dct
{'name': 'huoty'}
>>> dct.setdefault("fname", "esenich")
'esenich'
>>> dct
{'name': 'huoty', 'fname': 'esenich'}
>>> dct.setdefault("addr")
>>> dct
{'name': 'huoty', 'fname': 'esenich', 'addr': None}
>>> dct.get("name", "xxx")
'huoty'
>>> dct
{'name': 'huoty', 'fname': 'esenich', 'addr': None}
>>> dct.get("age")
>>> dct
{'name': 'huoty', 'fname': 'esenich', 'addr': None}
>>> dct.get("age", 2)
2
>>> dct
{'name': 'huoty', 'fname': 'esenich', 'addr': None}

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