Add a new item to a dictionary in Python

How do I add an item to an existing dictionary in Python? For example, given:

default_data = {
    'item1': 1,
    'item2': 2,
}

I want to add a new item such that:

default_data = default_data + {'item3': 3}

Answers:

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Method 1

default_data['item3'] = 3

Easy as py.

Another possible solution:

default_data.update({'item3': 3})

which is nice if you want to insert multiple items at once.

Method 2

It can be as simple as:

default_data['item3'] = 3

As Chris’ answer says, you can use update to add more than one item. An example:

default_data.update({'item4': 4, 'item5': 5})

Please see the documentation about dictionaries as data structures and dictionaries as built-in types.

Method 3

It occurred to me that you may have actually be asking how to implement the + operator for dictionaries, the following seems to work:

>>> class Dict(dict):
...     def __add__(self, other):
...         copy = self.copy()
...         copy.update(other)
...         return copy
...     def __radd__(self, other):
...         copy = other.copy()
...         copy.update(self)
...         return copy
... 
>>> default_data = Dict({'item1': 1, 'item2': 2})
>>> default_data + {'item3': 3}
{'item2': 2, 'item3': 3, 'item1': 1}
>>> {'test1': 1} + Dict(test2=2)
{'test1': 1, 'test2': 2}

Note that this is more overhead then using dict[key] = value or dict.update(), so I would recommend against using this solution unless you intend to create a new dictionary anyway.

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0