Get the key that has specific attribute of its value

Question

I have dictionary with list of objects as values.

class Device_Terminals():
    """Class for define object for each device"""
    def __init__(self, device_name, source, drain):
        self.device_name = device_name
        self.source = source
        self.drain = drain

device = Device_Terminals(line[0], line[1], line[3])
if line[2] not in devices_dict:
        devices_dict[line[2]] = []
devices_dict[line[2]].append(device)

I want to return the key whose one of its objects has specific name, the dictionary looks like this

{A1:[ MNA1 X_N1 VSS, MPA1_1 X X_P1_1, MPA1_2 X X_P1_2, MPA1_3 X X_P1_3, MPA1_4 X X_P1_4, MPA1_5 X X_P1_5, MPA1_6 X X_P1_6, MPA1_7 X X_P1_7], 'A3': [MNA3 X_N1 VSS, MPA3_1 X_P2_1 VDD, MPA3_2 X_P2_2 VDD, MPA3_3 X_P2_3 VDD, MPA3_4 X_P2_4 VDD, MPA3_5 X_P2_5 VDD]}

each element of the lists is an object. how can I return the key whose value of the

 device_name == MPA3_3: 
   return key

Please explain better what you’re looking for? Like what is `line` and what exactly you mean by `object` I’m not sure I fully understand where you’re going with this question. — Jab, Nov 12 '18 at 10:20
What is `device_dict`? You're question is not very clear. Please provide a reproductible example and a clear explanation of your issue, so other will be able to help you. — Antwane, Nov 12 '18 at 10:20
Can you please show the code that you use to construct the dictionary. Your data does not make sense as dicts have key value pairs. I don't see that in your update. Dicts are usually presented as `{key: value, key: value}`. — Ananth, Nov 12 '18 at 10:38
Possible duplicate of [Get key by value in dictionary](https://stackoverflow.com/questions/8023306/get-key-by-value-in-dictionary) — boonwj, Nov 12 '18 at 10:39
when I am trying to print it it looks like this {'A1': [<__main__.Device_Terminals instance at 0x7fce0b42ba70>, <__main__.Device_Terminals instance at 0x7fce0b42bb48>, <__main__.Device_Terminals instance at 0x7fce0b42bc20>] — M.salameh, Nov 12 '18 at 10:50
This is a dictionary with only one key (`A1`) and whose value is a list of `Device_Terminal` objects: where is the dict data you'r showing saved? Is this one of the `source`, `device` or `drain` field? — toti08, Nov 12 '18 at 10:59

score 1 · Accepted Answer · answered Nov 12 '18 at 11:08

You can create defaultdict from collections instead of checking if the key exists and then appending to it.

from collections import defaultdict
devices_dict = defaultdict(list)

To add to this dict:

device = Device_Terminals(line[0], line[1], line[3])
devices_dict[line[2]].append(device)

To search its values, you put a simple loop over the dictionary:

# your search term
search_val = 'device_name'
for key, devices in devices_dict.items():
    for device in devices:
        if search_val == device.device_name:
            print(key)

Thanks. This was very helpful! – M.salameh Nov 12 '18 at 11:18 — M.salameh, Nov 12 '18 at 11:18

score 0 · Answer 2 · answered Nov 12 '18 at 10:43

0

If you are trying to do dict lookup using its values. Try look at the solution of this previously answered question.

Get key by value in dictionary

answered Nov 12 '18 at 10:43

boonwj

356
1
10

but what if the value is object and I need specific attribute to compare with? @boonwj – M.salameh Nov 12 '18 at 10:50
Since values in the dictionary is not unique, you will need to loop through all values in the dictionary and get the data you need. – boonwj Nov 12 '18 at 10:58

Get the key that has specific attribute of its value

2 Answers2