How to Pythonically map content from one dict to another in a fail safe manner?
I've got one dict from an api:
initial_dict = {
"content": {
"text":
},
"meta": {
"title": "something",
"created": "2016-03-04 15:30",
"author": "Pete",
"extra": {
"a": 123,
"b": 456
}
}
}
and I need to map this to another dict:
new_dict = {
"content_text": initial_dict['content']['text'],
"meta_title": initial_dict['meta']['title'],
"meta_extras": {
"time_related": {
initial_dict['meta']['created']
},
"by": initial_dict['meta']['author']
}
}
The problem is that not all fields are always in the initial_dict. I can of course wrap the whole creation of new_dict into a try/except , but then it would fail if one of the initial fields doesn't exist.
Is there no other way than creating a try/except for each and every field I add to the new_dict ? In reality the dict is way bigger than this (about 400 key/value pairs), so this will become a mess quite fast.
Isn't there a better and more pythonic way of doing this?
How about using dict.get ? Instead of throwing an error, this returns None if the key isn't in the dictionary.
new_dict = {
"content_text": initial_dict['content'].get('text'),
"meta_title": initial_dict['meta'].get('title'),
"meta_extras": {
"time_related": {
initial_dict['meta'].get('created')
},
"by": initial_dict['meta'].get('author')
}
}
If this goes deeper than one level, you can do some_dict.get('key1', {}).get('key2') as was suggested in the comments.
Converting the original dict to a defaultdict is also an option, which allows you to keep using the [] notation (more practical than having to chain get methods):
from collections import defaultdict
def to_defaultdict(d):
return defaultdict(lambda: None, ((k, to_defaultdict(v) if isinstance(v, dict) else v)
for k, v in d.items()))
initial_dict = to_defaultdict(initial_dict)
You can then filter out the None values:
def filter_dict(d):
return dict((k, filter_dict(v) if isinstance(v, dict) else v)
for k, v in d.items() if v is not None)
new_dict = filter_dict(new_dict)
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