7.3. Staticmethod

7.3.1. Rationale

• Should not be in a class: method which don't use self in its body

• Should be in class: if method takes self and use it (it requires instances to work)

• If a method don't use self but uses class as a namespace use @staticmethod decorator

• Using class as namespace

• No need to create a class instance

• Will not pass instance (self) as a first method argument

class MyClass:

    @staticmethod
    def mymethod():
        pass


 MyClass.mymethod()

7.3.2. Example

class Astronaut:
    def __init__(self):
        self.name = 'José Jiménez'

    def say_hello(self):
        print(f'My name... {self.name}')

    @staticmethod
    def say_goodbye():
        print('Goodbye')

7.3.3. Instances

class MyClass:
    def say_hello(self):
        print(f'Hello')


my = MyClass()
my.say_hello()

class MyClass:
    @staticmethod
    def say_hello():
        print('Hello')

MyClass.say_hello()

7.3.4. Namespace

Functions on a high level of a module lack namespace:

def add(a, b):
    return a + b

def sub(a, b):
    return a - b


add(1, 2)
sub(8, 4)

When add and sub are in Calculator class (namespace) they get instance (self) as a first argument. Instantiating Calculator is not needed, as of functions do not read or write to instance variables:

class Calculator:

    def add(self, a, b):
        return a + b

    def sub(self, a, b):
        return a - b


Calculator.add(10, 20)
# Traceback (most recent call last):
# TypeError: add() missing 1 required positional argument: 'b'

Calculator.sub(8, 4)
# Traceback (most recent call last):
# TypeError: add() missing 1 required positional argument: 'b'

calc = Calculator()
calc.add(1, 2)
# 3
calc.sub(8, 4)
# 4

Class Calculator is a namespace for functions. @staticmethod remove instance (self) argument to method:

class Calculator:

    @staticmethod
    def add(a, b):
        return a + b

    @staticmethod
    def sub(a, b):
        return a - b


Calculator.add(1, 2)
Calculator.sub(8, 4)

7.3.5. Use Cases

Http Client:

class http:

    @staticmethod
    def get(url):
        ...

    @staticmethod
    def post(url, data):
        ...

http.get('https://python.astrotech.io')
http.post('https://python.astrotech.io', data={'astronaut': 'Mark Watney'})

Astronaut Hello:

def astronaut_say_hello():
    print('hello')

def astronaut_say_goodbye():
    print('goodbye')


class Astronaut:
    pass


a = Astronaut()
astronaut_say_hello()
# hello
astronaut_say_goodbye()
# 'goodbye'

class Astronaut:
    def say_hello(self):
        print('hello')

    def say_goodbye(self):
        print('goodbye')


a = Astronaut()
a.say_hello()
# hello
a.say_goodbye()
# 'goodbye'

Astronaut.say_hello()
# Traceback (most recent call last):
# TypeError: say_hello() missing 1 required positional argument: 'self'

Astronaut.say_goodbye()
# Traceback (most recent call last):
# TypeError: say_goodbye() missing 1 required positional argument: 'self'

class Astronaut:

    @staticmethod
    def say_hello():
        print('hello')

    @staticmethod
    def say_goodbye():
        print('goodbye')


Astronaut.say_hello()
# hello

Astronaut.say_goodbye()
# 'goodbye'

astro = Astronaut()
astro.say_hello()
# hello
astro.say_goodbye()
# goodbye

Helper HabitatOS Z-Wave sensor model:

from datetime import datetime, timezone
from decimal import Decimal, InvalidOperation
import logging

from django.db import models
from django.utils.translation import ugettext_lazy as _

from habitat._common.models import HabitatModel
from habitat._common.models import MissionDateTime
from habitat.time import MissionTime

log = logging.getLogger('habitat.sensor')


def clean_unit(unit: str) -> str:
    try:
        return {
            'C': 'celsius',
            'F': 'fahrenheit',
            'dB': 'decibel',
            'lux': 'lux',
            '%': 'percent',
        }[unit]
    except KeyError:
        return None


def clean_type(type: str) -> str:
    return type.lower().replace(' ', '-')


def clean_value(value: str) -> Decimal:
    try:
        return Decimal(value)
    except InvalidOperation:
        return Decimal(0)


def clean_device(device: str) -> str:
    return device


def clean_datetime(dt: str) -> datetime:
    try:
        return datetime.strptime(dt, '%Y-%m-%d %H:%M:%S.%f+00:00').replace(tzinfo=timezone.utc)
    except ValueError:
        return datetime.strptime(dt, '%Y-%m-%d %H:%M:%S.%f')


class ZWaveSensor(HabitatModel, MissionDateTime):
    TYPE_BATTERY_LEVEL = 'battery-level'
    TYPE_POWER_LEVEL = 'powerlevel'
    TYPE_TEMPERATURE = 'temperature'
    TYPE_LUMINANCE = 'luminance'
    TYPE_RELATIVE_HUMIDITY = 'relative-humidity'
    TYPE_ULTRAVIOLET = 'ultraviolet'
    TYPE_BURGLAR = 'burglar'
    TYPE_CHOICES = [
        (TYPE_BATTERY_LEVEL, _('Battery Level')),
        (TYPE_POWER_LEVEL, _('Power Level')),
        (TYPE_TEMPERATURE, _('Temperature')),
        (TYPE_LUMINANCE, _('Luminance')),
        (TYPE_RELATIVE_HUMIDITY, _('Relative Humidity')),
        (TYPE_ULTRAVIOLET, _('Ultraviolet')),
        (TYPE_BURGLAR, _('Burglar'))]

    UNIT_CELSIUS = 'celsius'
    UNIT_KELVIN = 'kelvin'
    UNIT_FAHRENHEIT = 'fahrenheit'
    UNIT_DECIBEL = 'decibel'
    UNIT_LUMINANCE = 'lux'
    UNIT_PERCENT = 'percent'
    UNIT_DIMENSIONLESS = None
    UNIT_CHOICES = [
        (UNIT_DIMENSIONLESS, _('n/a')),
        (UNIT_PERCENT, _('%')),
        (UNIT_LUMINANCE, _('Lux')),
        (UNIT_DECIBEL, _('dB')),
        (UNIT_CELSIUS, _('°C')),
        (UNIT_KELVIN, _('K')),
        (UNIT_FAHRENHEIT, _('°F'))]

    DEVICE_ATRIUM = 'c1344062-2'
    DEVICE_ANALYTIC_LAB = 'c1344062-3'
    DEVICE_OPERATIONS = 'c1344062-4'
    DEVICE_TOILET = 'c1344062-5'
    DEVICE_DORMITORY = 'c1344062-6'
    DEVICE_STORAGE = 'c1344062-7'
    DEVICE_KITCHEN = 'c1344062-8'
    DEVICE_BIOLAB = 'c1344062-9'
    DEVICE_AIRLOCK = None
    DEVICE_CHOICES = [
        (DEVICE_ATRIUM, _('Atrium')),
        (DEVICE_ANALYTIC_LAB, _('Analytic Lab')),
        (DEVICE_OPERATIONS, _('Operations')),
        (DEVICE_TOILET, _('Toilet')),
        (DEVICE_DORMITORY, _('Dormitory')),
        (DEVICE_STORAGE, _('Storage')),
        (DEVICE_KITCHEN, _('Kitchen')),
        (DEVICE_BIOLAB, _('Biolab'))]

    datetime = models.DateTimeField(verbose_name=_('Datetime [UTC]'), db_index=True)
    device = models.CharField(verbose_name=_('Sensor Location'), max_length=30, choices=DEVICE_CHOICES, db_index=True)
    type = models.CharField(verbose_name=_('Type'), max_length=30, choices=TYPE_CHOICES)
    value = models.DecimalField(verbose_name=_('Value'), max_digits=7, decimal_places=2, default=None)
    unit = models.CharField(verbose_name=_('Unit'), max_length=15, choices=UNIT_CHOICES, null=True, blank=True, default=None)

    def __str__(self) -> str:
        return f'[{self.date} {self.time}] (device: {self.device}) {self.type}: {self.value} {self.unit}'

    class Meta:
        verbose_name = _('Data')
        verbose_name_plural = _('Zwave Sensors')

    @staticmethod
    def add(datetime: str, device: str, type: str, value: str, unit: str):
        dt = clean_datetime(datetime)
        time = MissionTime().get_time_dict(from_datetime=dt)
        data = {'date': time['date'],
                'time': time['time'],
                'device': clean_device(device),
                'type': clean_type(type),
                'value': clean_value(value),
                'unit': clean_unit(unit)}
        return ZWaveSensor.objects.update_or_create(datetime=dt, defaults=data)

from habitat.time import MissionTime
from habitat.sensors.models import ZWaveSensor
from habitat.sensors.models import clean_datetime
from habitat.sensors.models import clean_device
from habitat.sensors.models import clean_type
from habitat.sensors.models import clean_value
from habitat.sensors.models import clean_unit


dt = clean_datetime(datetime)
time = MissionTime().get_time_dict(from_datetime=dt)
data = {'date': time['date'],
        'time': time['time'],
        'device': clean_device(device),
        'type': clean_type(type),
        'value': clean_value(value),
        'unit': clean_unit(unit)}

obj = ZWaveSensor.objects.update_or_create(datetime=dt, defaults=data)

obj = ZWaveSensor.add(datetime, device, type, value, unit)

7.3.6. Assignments