KnowCardPython · The collections Module
What's the difference between Counter.update(other) and Counter.subtract(other) when combining two counters?
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More in The collections Module
When should you prefer dict.setdefault(k, []).append(x) over a defaultdict(list)?
You need to look up scores by team name when the data is split across several separate dicts (group_a, group_g, ...). You don't want to merge them into a new dict. Which collections type fits?
What does this print?
```
from collections import ChainMap
a = {"x": 1}
b = {"x": 2, "y": 9}
cm = ChainMap(a, b)
print(cm["x"], cm["y"])
```
With cm = ChainMap(a, b), you do cm["x"] = 100. Which underlying dict gets modified?
You want to count how often each character appears in a string, with the least code. Which collections type, and how in one line?
What does this print?
```
from collections import Counter
c = Counter("aabbbc")
print(c["z"])
print("z" in c)
```
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