Code Explanation:
1. 📦 Import ChainMap
from collections import ChainMap
ChainMap comes from Python's collections module.
It allows multiple dictionaries to be treated as a single mapping.
2. 🗂️ Create Dictionary a
a = {"x": 1}
Dictionary a contains:
x → 1
3. 🗂️ Create Dictionary b
b = {"x": 2}
Dictionary b contains:
x → 2
Both dictionaries have the same key "x".
4. 🔗 Create the ChainMap
c = ChainMap(a, b)
The lookup order is:
c
↓
a → {"x": 1}
↓
b → {"x": 2}
The first mapping has priority.
Therefore:
c["x"]
returns:
1
because "x" is found in a first.
5. ➕ Update c["x"]
c["x"] += 5
This is effectively:
c["x"] = c["x"] + 5
First, Python reads:
c["x"] → 1
Then:
1 + 5 = 6
Now Python assigns the result back through the ChainMap:
c["x"] = 6
6. 🎯 Where Does the Update Go?
This is the important part.
ChainMap writes changes to its first mapping.
So:
a["x"] → 6
b["x"] → 2
b remains unchanged.
7. 🖨️ Print the Values
print(a["x"], b["x"])
Now:
a["x"] = 6
b["x"] = 2
Therefore:
✅ Final Output
6 2
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