How to create if-else statements on dicts with missing keys

Question

I want to create an if-else condition on dictionaries with missing keys. Such that, if the key is missing then append the value None, otherwise append the data when it exists.

However, this approach would stop with an error as when the key does not exist it seems to not return True or False.

For example:

df = [{'data':'test', 'videos':5, 'likes':4}, {'data':'test','likes':4}]
videos = []
for i in df:
    if i['videos']:
        videos.append(i)
    elif i['videos'] is not True:
        videos.append('None')

Output:

{'data': 'test', 'videos': 5, 'likes': 4}
---------------------------------------------------------------------------
KeyError                                  Traceback (most recent call last)
/var/folders/dr/9wh_z8y10fl79chj86pq7knc0000gn/T/ipykernel_3180/3991749010.py in <module>
      1 df = [{'data':'test', 'videos':5, 'likes':4}, {'data':'test','likes':4}]
      2 for i in df:
----> 3     if i['videos']:
      4         print(i)
      5     elif i['videos'] is not True:

KeyError: 'videos'

Does this answer your question? [Return None if Dictionary key is not available](https://stackoverflow.com/questions/6130768/return-none-if-dictionary-key-is-not-available) — Kelly Bundy, Feb 16 '22 at 00:41
You can use this https://docs.python.org/3/library/stdtypes.html#dict.get — Developer, Feb 16 '22 at 00:43

score 2 · Answer 1 · answered Feb 16 '22 at 00:48

2

I would go for a list comprehension using .get() method of Python's dictionaries as this one would return None by default if the requested key is missing:

df = [{'data':'test', 'videos':5, 'likes':4}, {'data':'test','likes':4}]

videos = [e.get("videos") for e in df]

answered Feb 16 '22 at 00:48

daniel451

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Output `[5, None]` as expected? – hc_dev Feb 16 '22 at 01:42
@hc_dev yes, indeed. – daniel451 Feb 16 '22 at 01:53
I don't think this is the desired output. – Wups Feb 16 '22 at 08:42

score 1 · Accepted Answer · answered Feb 16 '22 at 00:45

1

Just check if the key is actually in dict.keys()

df = [{'data':'test', 'videos':5, 'likes':4}, {'data':'test','likes':4}]
videos = []
for i in df:
    if 'video' in i.keys():
        videos.append(i)
    else:
        videos.append('None')

answered Feb 16 '22 at 00:45

Synthase

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This works great! a few issues with the code output but I managed to reconfigure it to my needs. Thanks! – dollar bill Feb 16 '22 at 00:46

hc_dev · Answer 3 · 2022-02-16T07:45:21.463

TL;DR: Use the defaulting getter dict.get(key, default) like videos.append(i.get('videos', 'None')).

Lookup by key in a dict

string-indexing a dict entry will always raise KeyError if the key was not found.

Use the safe dict.get(key) method which returns None as default if key is not found.

See also: Why dict.get(key) instead of dict[key]?

Make your code simpler and robust

Your if-statement could be simplified to:

video = i.get('videos')   # use a safe get by key
videos.append(video if video else 'None')  # if not found, then default string

The construct x if condition else y is called conditional expression (ternary operation) - not to confuse with Elvis operator: Does Python have the Elvis operator?

Just for the completeness to catch and handle a KeyError is also an option:

try:
    video = i['videos']   # unsafe may raise KeyError
except KeyError:
    video = 'None'  # default
videos.append(video)  # after the try-except the video is guaranteed to have a string

See the Python tutorial: Try and Except in Python

@KellyBundy Thanks for proof-reading and the clarification to learn. Added links and fixed it. — hc_dev, Feb 16 '22 at 07:46

score 0 · Answer 4 · answered Feb 16 '22 at 01:40

Ah ... now I understood. You just want to filter the list for items that contain 'videos' ?!

Maybe use the filter function. See my demo on interactive Python shell:

>>> df = [{'data':'test', 'videos':5, 'likes':4}, {'data':'test','likes':4}]
>>> list(filter(lambda i: i.get('videos') is not None, df))
[{'data': 'test', 'videos': 5, 'likes': 4}]

Note: the return of filter is a filter-object which needs to be converted using list().

How to create if-else statements on dicts with missing keys

4 Answers4

Lookup by key in a dict

Make your code simpler and robust