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54 lines
1.6 KiB
Markdown
54 lines
1.6 KiB
Markdown
---
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title: "Quick Python: Getters and Setters"
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date: 2020-04-08T18:15:21-04:00
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draft: false
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tags: ["Python"]
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medium_enabled: true
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---
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One of the hidden gems in Python classes are seamless getters and setters. I discovered this through the book [Effective Python by Brett Slatkin](https://effectivepython.com/). Though the example I'll use is different and shorter than the one he uses in his book.
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Let's create a class representing a person. The only information we're going to store is their age and we'll make it optional to provide it.
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```python
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class Person:
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def __init__(self, age=None):
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self._age = None
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@property
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def age(self):
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if self._age is None:
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raise ValueError("age must be set before accessing it.")
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return self._age
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@age.setter
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def age(self, age):
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if age < 0:
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raise ValueError("age must be at least zero.")
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self._age = age
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```
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The second function in the class decorated by `@property` will be the getter function for the attribute `_age`. The name of the function will be what we expect the user to access it as. The setter is then decorated with `age.setter` where `age` is the name of the attribute. As such the name chosen in the getter function name, setter function name, and decorator must all match.
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Now let's try using it
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```python
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bobby = Person()
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bobby.age
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```
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```
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Traceback (most recent call last):
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File "<stdin>", line 1, in <module>
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File "/home/user/test.py", line 7, in age
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raise ValueError("age must first be set before accessing it")
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ValueError: age must first be set before accessing it
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```
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```python
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bobby.age = 5
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bobby.age
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```
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```
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5
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```
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