KnowCardPython · The Data Model: Identity & Mutability
The correct, idiomatic way to test whether a variable is None: x == None or x is None?
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Predict the output:
```
v1 = [1, 2, 3]
v2 = v1
v3 = [1, 2, 3]
print(v1 == v3, v1 is v3)
print(v1 == v2, v1 is v2)
```
Every non-speed: a colleague checks if x is 1000: and it returns False even though x == 1000. What's the rule that explains both this and why x is 256 sometimes 'works'?
Does assignment b = a copy the object that a refers to?
Predict the output:
```
a = "water "
b = a
a += "bottle"
print(a)
print(b)
```
Predict the output:
```
a = [1, 2]
b = a
a += [3, 4]
print(a)
print(b)
```
Why does the SAME += line leave an aliased str untouched but mutate an aliased list?
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