Properties in Python

Attribute syntax with method power: computed and guarded fields.

class Temperature:
    def __init__(self, celsius=0):
        self._celsius = celsius

    @property
    def celsius(self):
        return self._celsius

    @celsius.setter
    def celsius(self, value):
        if value < -273.15:
            raise ValueError("below absolute zero")
        self._celsius = value

    @property
    def fahrenheit(self):
        return self._celsius * 9 / 5 + 32

How it works

1. @property makes celsius readable like a plain attribute.
2. The setter validates before storing.
3. fahrenheit is computed fresh on every read.

Keywords and builtins used here

• Temperature
• celsius
• class
• def
• fahrenheit
• if
• raise
• return
• self

The run, in numbers

Lines

17

Characters to type

316

Tokens

75

Three-star pace

95 tpm

At the three-star pace of 95 tokens a minute, this run takes about 47 seconds.

Type this snippet

Step 3 of 5 in Classes, step 41 of 72 in Language basics.

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