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When using the update function for a dictionary in python where you are merging two dictionaries and the two dictionaries have the same keys they are apparently being overwritten.

A simple example:

simple_dict_one = {'name': "tom", 'age': 20}
simple_dict_two = {'name': "lisa", 'age': 17}
simple_dict_one.update(simple_dict_two)

After the dicts are merged the following dict remains:

{'age': 17, 'name': 'lisa'}

So if you have the same key in both dict only one remains (the last one apparently). If i have a lot of names for several sources i would probably want a temp dict from each of those and then want to add it to a whole bigger dict.

Is there a way to merge two dicts and still keep all the keys ? I guess you are only suppose to have one unique key but then how would i merge two dicts without loosing data

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    It looks like what you're trying to do is *not* to merge two dictionaries. You have a dictionary for each person with keys for their name and age. If you merged them you would lose the association between the name and the age belonging to the same person. What are you actually trying to do? – khelwood Oct 22 '14 at 11:05
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    What is your desired output? – Daniel Roseman Oct 22 '14 at 11:06
  • Well i have several sources i gather information from, for example an ldap database and other sources where i have python functions that create a temp dict each but i want a complete dict at the end that sort of concatenates or displays all information gathered from all the sources.. so i would have one dict holding all the info –  Oct 22 '14 at 11:13
  • Is there any reason you dont want to have that information in a list of dicts? – Tim Oct 22 '14 at 11:23
  • hmm thats interesting, i didnt even think of that, thats fine though and might be a lot easier, better and more pythonic? –  Oct 22 '14 at 11:27
  • Related: http://stackoverflow.com/questions/11011756/is-there-any-pythonic-way-to-combine-two-dicts-adding-values-for-keys-that-appe – Bakuriu Oct 22 '14 at 11:44

1 Answers1

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Well i have several sources i gather information from, for example an ldap database and other sources where i have python functions that create a temp dict each but i want a complete dict at the end that sort of concatenates or displays all information gathered from all the sources.. so i would have one dict holding all the info

What you are trying to do with the 'merging' is not quite ideal. As you said yourself

I guess you are only suppose to have one unique key

Which makes it relatively and unnecessarily hard to gather all your information in one dict.
What you could do, instead of calling .update() on the existing dict, is add a sub-dict. Its key could be the name of the source from which you gathered the information. The value could be the dict you receive from the source, and if you need to store more than 1 dict of the same source you can store them in a list.

Example

>>> data = {}
>>> person_1 = {'name': 'lisa', 'age': 17}
>>> person_2 = {'name': 'tom', 'age': 20}
>>> data['people'] = [person_1, person_2]
>>> data
{'people': [{'age': 17, 'name': 'lisa'}, {'age': 20, 'name': 'tom'}]}

Then whenever you need to add newly gathered information, you just add a new entry to the data dict

>>> ldap_data = {'foo': 1, 'bar': 'baz'} # just some dummy data
>>> data['ldap_data'] = ldap_data
>>> data
{'people': [{'age': 17, 'name': 'lisa'}, {'age': 20, 'name': 'tom'}],
 'ldap_data': {'foo': 1, 'bar': 'baz'}}

The source-specific data is easily extractable from the data dict

>>> data['people']
[{'age': 17, 'name': 'lisa'}, {'age': 20, 'name': 'tom'}]

>>> data['ldap_data']
{'foo': 1, 'bar': 'baz'}
Tim
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