🏫 [CS50x 2025] 6 Python

Check if a dict is a subset of another dict

Option 1: Do all keys & values in crime_gene appear in p?

if all(p.get(k) == v for k, v in crime_gene.items()):
    return True

This checks:

• For every gene in crime_gene, does p have the same value?
• It’s doing a field-by-field match - very forensics-style

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Option 2: Check if crime_gene.items() is a subset of p.items()?

if crime_gene.items() <= p.items():
    return True

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Example

crime_gene = {'AGATC': '2', 'AATG': '8', 'TATC': '3'}
p = {'name': 'Alice', 'AGATC': '2', 'AATG': '8', 'TATC': '3'}

# Both of these work:
if all(p.get(k) == v for k, v in crime_gene.items()):
    return True

# OR:
if crime_gene.items() <= p.items():
    return True

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if all(p.get(k) == v for k, v in crime_gene.items()):

For every gene in crime_gene, check if p has the same key with the same value. If all of them match, return True, otherwise nope.

for k, v in crime_gene.items()

This part loops over every key: value pair in crime_gene. Think of it like:

for k, v in [('AGATC', '2'), ('AATG', '8'), ('TATC', '3')]:

So:

• k = 'AGATC', v = '2'
• k = 'AATG', v = '8'
• …

p.get(k) == v

For each key in crime_gene, we’re checking:

Does p have this same key, and is the value the same?

p.get(k) is safer than p[k] because it won’t throw an error if the key doesn’t exist—it’ll return None.

So for example:

p.get('AGATC') == '2'  → ✅
p.get('AATG') == '8'   → ✅
p.get('TATC') == '3'   → ✅

all(...)

The all() function checks:

Are ALL these expressions True?

If even one is False, then all() returns False.