Python list Comprehension inside dictionaries

Question

I have a dictionary inside list like this:

a = [{'valid': True, 'power': None, 'altitude': 0.0, 'time': datetime.datetime(2014, 4, 7, 16, 5, 55), 'longitude': 47.938, 'course': 0.0, 'address': None, 'latitude': 29.3309, 'speed': 0.0, u'id': 3L, 'device_id': 1L}]

I only want to play with time key and put everything same. For example:

[i+timedelta(5) for i in a]

This works but return time on list like this: [.........] which is understandable. But what I want is:

Change the value of time on the original list itself like:

a = [{'valid': True, 'power': None, 'altitude': 0.0, 'time': NEW VALUE, 'longitude': 47.938, 'course': 0.0, 'address': None, 'latitude': 29.3309, 'speed': 0.0, u'id': 3L, 'device_id': 1L}]

How to do this?

Ashwini Chaudhary · Accepted Answer · 2014-04-25 12:49:54Z

2

Use a simple for-loop. List comprehensions are used to create new lists, don't use them for side-effects.

it = iter(dct['time'] for dct in a) tot = sum(it, next(it)) for dct in a: dct['time'] = tot

Another way to sum the dates will be to use reduce()(functools.reduce in Python 3):

>>> dates = [dct['time'] for dct in a] >>> reduce(datetime.datetime.__add__, dates) datetime.datetime(2014, 4, 7, 16, 5, 55)

edited Apr 25, 2014 at 12:49

answered Apr 25, 2014 at 12:06

Ashwini Chaudhary

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8 Comments

pynovice Over a year ago

But How to get individual values of time and add.

Ashwini Chaudhary Over a year ago

@user2032220 I don't understand what you meant by individual values of time. And please don't delete the question once you've got your answer, I almost reported this to a moderator.

pynovice Over a year ago

My list has more than one dictionary, I want to add to every time field.

Ashwini Chaudhary Over a year ago

@user2032220 You mean replace all the time fields with the total time?

pynovice Over a year ago

Yes, that's what I meant.

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Oleg Sklyar · Accepted Answer · 2014-04-25 13:01:50Z

Make sure you return an element, which is dictionary in this case. Otherwise your dictionary might get updated (if written correctly), but will not reappear as an element of the resulting list:

def update(item_dict): item_dict['time'] = item_dict['time'] + timedelta(5) return item_dict [update(item_dict) for item_dict in a]

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