Hi Pythonistas!
When working with dictionaries, one common headache is handling missing keys.Manually checking and initializing every key clutters your code.
Instead, Python offers a beautiful tool: defaultdict from the collections module!
The Old (Tedious) Way: Manual Checks
In [4]: words = ['apple', 'banana', 'apple', 'orange', 'banana', 'apple']
In [5]: word_counts = {}
In [6]: for word in words:
...: if word not in word_counts:
...: word_counts[word] = 1
...: else:
...: word_counts[word] += 1
...:
In [7]: word_counts
Out[7]: {'apple': 3, 'banana': 2, 'orange': 1}
In [8]:
✅ Works, but the manual checking (if word not in word_counts) is extra noise.
❌ Harder to read, harder to maintain.
The Better Way: Use defaultdict
In [9]: from collections import defaultdict
...:
...: words = ['apple', 'banana', 'apple', 'orange', 'banana', 'apple']
...:
...: word_counts = defaultdict(int)
...: for word in words:
...: word_counts[word] += 1
...:
...: print(word_counts)
defaultdict(<class 'int'>, {'apple': 3, 'banana': 2, 'orange': 1})
In [10]:
In [10]: ✅ Cleaner
✅ Shorter
✅ Focuses purely on counting words!
How defaultdict Works
If you try to access a missing key, it automatically creates a default value (like 0, [], set(), etc.)
No manual checks needed. It calls the function you specify (like int, list, set) to create the missing value.
Grouping Made Easy
In [10]: names = ['Alice', 'Bob', 'Alice', 'David', 'Bob']
...:
...: groups = defaultdict(list)
...: for name in names:
...: groups[name[0]].append(name)
...:
In [11]: groups
Out[11]:
defaultdict(list,
{'A': ['Alice', 'Alice'], 'B': ['Bob', 'Bob'], 'D': ['David']})
Grouping by the first letter — and no need to initialize lists manually! ✨
✅ Best Practice
Prefer defaultdict when you're handling missing keys.Use appropriate default factories like int, list, or set.
Cleaner code = fewer bugs + happier future you.