Python Store and Count Items with Dictionary Values

A supply room counts labels recorded in a delivery.

What You Need to Understand

A dictionary can count repeated items by using each item as a key and storing its count as the value. Use get(item, 0) + 1 to handle the first occurrence.

When to Use It

A supply room counts labels recorded in a delivery.

Step-by-Step Python Example

items = ["pen", "folder", "pen", "paper", "pen"]
counts = {}
for item in items:
    counts[item] = counts.get(item, 0) + 1
for item in sorted(counts):
    print(item, counts[item])

How the Example Works

Every occurrence increments the appropriate value; the final dictionary contains one key per distinct item.

Example Output

folder 1
paper 1
pen 3
a

A Second Example

Compare this smaller variation with the main example, then experiment with your own values.

items = ["a", "b", "a"]
counts = {}
for item in items:
    counts[item] = counts.get(item, 0) + 1
print(max(counts, key=counts.get))

Important Behavior and Edge Cases

Keys are case-sensitive. Normalize first only when Pen and pen should be the same product; avoid counting display labels that are not reliable identifiers.

Try It Yourself

Find the most frequent label in a short list using the counts dictionary.

Common Beginner Mistakes

Keys are case-sensitive. Normalize first only when Pen and pen should be the same product; avoid counting display labels that are not reliable identifiers.
Applying the example without a clearly defined policy for missing keys, matching identifiers, or validating external values.

Key Takeaways

A dictionary can count repeated items by using each item as a key and storing its count as the value.
Every occurrence increments the appropriate value; the final dictionary contains one key per distinct item.
Keys are case-sensitive.