Not able to understand code behaviour - python

Question

I just started with python , and now I am trying to understand dictionary comprehension , but I don't get the behaviour of the following code :

    data = [
             {'id': 12, 'data': '01'},
             {'id': 10, 'data': '05'},
             {'id': 11, 'data': '07'},
           ]
             { d['id']:d for d in data }.values()

Output :

dict_values([{'id': 12, 'data': '01'}, {'id': 10, 'data': '05'}, {'id': 11, 'data': '07'}])

please explain the output for the mentioned code . Why it is printing 2nd key value pair of each dictionary of data i.e. 'data':'01' and so on.

Emipro Technologies Pvt. Ltd. · Accepted Answer · 2017-03-26 17:52:36Z

2

You have create list of dict

data = [ {'id': 12, 'data': '01'}, {'id': 10, 'data': '05'}, {'id': 11, 'data': '07'}, ]

If we split first statement then we will get following result.

{ d['id']:d for d in data }

{10: {'data': '05', 'id': 10}, 11: {'data': '07', 'id': 11}, 12: {'data': '01', 'id': 12}}

d is you first dict & you are creating new dict with d[id]

d['id']:d -> 10: {'data': '05', 'id': 10}

values() : This method returns a list of all the values available in a given dictionary.

In your example 3 dict are values.

That's why you are getting result like.

[{'data': '05', 'id': 10}, {'data': '07', 'id': 11}, {'data': '01', 'id': 12}]

edited Mar 26, 2017 at 17:52

answered Mar 26, 2017 at 17:45

Emipro Technologies Pvt. Ltd.

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1 Comment

idjaw Over a year ago

You should use the code formatting for the code parts.

WNG · Accepted Answer · 2017-03-26 17:40:46Z

data is an array that contains 3 dictionnaries, each one having 2 keys : "id" and "data".

What you are asking python is :

{ d['id']:d for d in data }

"Build me a dictionnary that contains 1 pair key/value for each element of my data array. Each key should be the "id" value of this element, and each value should be the element of d itself"

What you probably want to do is :

In [6]: c={ d['id']:d["data"] for d in data}

In [7]: c
Out[7]: {10: '05', 11: '07', 12: '01'

"Build me a dictionnary that contains 1 pair key/value for each element of my data array. Each key should be the "id" value of this element, and each value should be the "data" value of of this element"

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