python: override a single dict key based on a separate dict

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Check if a given key already exists in a dictionary 18 answers

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Just try to replace it. This avoids one unnecessary hashing (compared to using if 'day' in query: ) or looping over the dictionary and follows Pythons EAFP principle:

try:
    query['day'] = day_mapping[query['day']]
except KeyError:
    pass

---

You may use dict.get(..) to check for the presence of 'day' key in your dict as:

query = {'day': 0, 'item': 'Chipotle'}
day_mapping = {0:2, 1:3, 2:4, 3:5, 4:6, 5:7, 6:1}

day = query.get('day')  # returns `None` if 'day' key not found in `dict`
if day is not None:
    query['day'] = day_mapping[day]

Updated value of query dict in above example will be:

{'day': 2, 'item': 'Chipotle'}

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