从字典列表到字典

Question

I have some problem with my function.

I do an SQL Query to obtain a list that have some dictionary with only a key/value element. This is a sample of my output:

myDictList = [{'id': 55, 'sigla': 'SNG'}, {'id': 62, 'sigla': 'TRP'}, 
 {'id': 71, 'sigla': 'PCNIM'},  {'id': 72, 'sigla': 'pc2ni'}, 
 {'id': 73, 'sigla': 'ccas'}, {'id': 74, 'sigla': 'ased1'}, 
 {'id': 75, 'sigla': '131s'}, {'id': 76, 'sigla': 'r888'}, 
 {'id': 56, 'sigla': 'DBL'}]

The id are unique (for SQL constraint).

I've build a list of id in that way

r_id_list = list(rid['id'] for rid in roomList)

Now, i would build a dict. like that from myDictList :

{55:'SNG',62:'TRP',71:'PCNIM'.... and so on}

More over, i want to avoid part of code like that:

finalDict = {}
for element in myDictList:
    finalDict.update({element['id']:element['sigla']})

I want to do that for some reasons:

• I don't want to do two separate query to obtain some data that i can retrive with one
• I don't want to iterate to every list element for retrive sigla value from r_id_list element

Some suggestion for a compact code that will not include a for cycle inside a for cycle, and increase the complexity?

Answer 1

finalDict = dict([(k['id'], k['sigla']) for k in myDictList])

EDIT1 As comment mentioned, it will be a better way to do.

finalDict = dict(((k['id'], k['sigla']) for k in myDictList))

EDIT2

finalDict = dict((k['id'], k['sigla']) for k in myDictList)

Answer 2

将dict（）构造函数与生成器表达式一起使用：

finalDict = dict((elem['id'], elem['sigla']) for elem in myDictList)

Answer 3

finaldict = {k['id']: k['sigla'] for k in myDictList}

if you're on a current version of Python. Dictionary comprehensions have been introduced in Python 3 and backported to Python 2.7:

Python 2.7.2 (default, Jun 12 2011, 14:24:46) [MSC v.1500 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> myDictList = [{'id': 55, 'sigla': 'SNG'}, {'id': 62, 'sigla': 'TRP'},
...  {'id': 71, 'sigla': 'PCNIM'},  {'id': 72, 'sigla': 'pc2ni'},
...  {'id': 73, 'sigla': 'ccas'}, {'id': 74, 'sigla': 'ased1'},
...  {'id': 75, 'sigla': '131s'}, {'id': 76, 'sigla': 'r888'},
...  {'id': 56, 'sigla': 'DBL'}]
>>> {k['id']: k['sigla'] for k in myDictList}
{71: 'PCNIM', 72: 'pc2ni', 73: 'ccas', 74: 'ased1', 75: '131s', 76: 'r888', 55:'SNG', 56: 'DBL', 62: 'TRP'}

Answer 4

Consider taking a step back here and looking outside the narrow focus of the question. You say "I do an SQL Query to obtain a list that have some dictionary". What are you using to do the SQL query?

By default Python database drivers return a tuple for each row rather than dict , so you presumably have some other code which is converting those tuples into a dict before you want to convert them back again. Your best bet would be to just do a query that returns tuples and construct your dict directly from that:

cursor.execute('SELECT id, sigla FROM sometable')
myDict = dict(cursor.fetchall())

Answer 5

res_dict = {}
for i in myDictList:
    res_dict[i['id']] = i['sigla']

Answer 6

As others have already pointed out the best way to build your final dictionary is using a generator expression like:

finalDict = dict((d['id'], d['sigla']) for d in myDictList)

And if you still need an iterable over your ids you can have that just calling finalDict.keys() .