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content/blog/pygetset.md

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+---
+title: "Quick Python: Getters and Setters"
+date: 2020-04-08T18:15:21-04:00
+draft: false
+tags: ["python"]
+---
+
+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.
+
+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.
+
+```python
+class Person:
+    def __init__(self, age=None):
+        self._age = None
+    @property
+    def age(self):
+        if self._age is None:
+            raise ValueError("age must be set before accessing it.")
+        return self._age
+   	@age.setter
+    def age(self, age):
+        if age < 0:
+            raise ValueError("age must be at least zero.")
+        self._age = age
+```
+
+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.
+
+Now let's try using it
+
+```python
+bobby = Person()
+bobby.age
+```
+
+```
+Traceback (most recent call last):
+  File "<stdin>", line 1, in <module>
+  File "/home/user/test.py", line 7, in age
+    raise ValueError("age must first be set before accessing it")
+ValueError: age must first be set before accessing it
+```
+
+```python
+bobby.age = 5
+bobby.age
+```
+
+```
+5
+```
+