45 lines
1.1 KiB
Markdown
45 lines
1.1 KiB
Markdown
---
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tags: [python, data-types]
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---
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# None in Python
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`None` is not `null`, it is closer to `undefined` in JS. If you define a
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variable as `None`, the variable exists, it is just not yet defined.
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Using `None` is a pattern similar to using `let` in JS to name a variable and
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definine it later on.
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```python
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temperature = None
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```
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If we logged `temperature` it would give us `None` rather than a null pointer
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error.
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With None we can use `is None` and `is not None`, special predicates for working
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with `None` only. This is a akin to using `if (x !== undefined)` in TypeScript
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```python
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winner = None
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print('winner:', winner)
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# winner: None
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print('winner is None:', winner is None)
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# winner is None: True
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print('winner is not None:', winner is not None)
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# winner is not None: False
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print(type(winner))
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# <class 'NoneType'>
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# Now set winner to be True
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print('Set winner to True')
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# Set winner to True
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winner = True
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print('winner:', winner)
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# winner: True
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print('winner is None:', winner is None)
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# winner is None: False
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print('winner is not None:', winner is not None)
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# winner is not None: True
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print(type(winner))
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# <class 'bool'>
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```
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