SOLID Principles Python examples

main.ipynb

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    "# SOLID Principles example\n",
    "\n",
    "\n",
    "## 1. Single Responsibility Principle\n",
    "\n",
    "\n",
    "### 1.1 Single Responsibility Principle violation\n",
    "\n",
    "```python\n",
    "class Animal:\n",
    "    def __init__(self, name):\n",
    "        self.name = name\n",
    "\n",
    "    def make_sound(self):\n",
    "        print(self.name, \"makes sound...\")\n",
    "\n",
    "    @classmethod\n",
    "    def get_from_db(cls, name):\n",
    "        print(\"find\", name, \"in db\", cls)\n",
    "\n",
    "    def save_to_db(self):\n",
    "        print(\"save to db\", self)\n",
    "```\n",
    "\n",
    "\n",
    "### 1.2 Following the Single Responsibility Principle\n",
    "\n",
    "\n",
    "```python\n",
    "class Animal:\n",
    "    def __init__(self, name):\n",
    "        self.name = name\n",
    "\n",
    "    def make_sound(self):\n",
    "        print(self.name, \"makes sound...\")\n",
    "\n",
    "\n",
    "class AnimalDB:\n",
    "\n",
    "    @classmethod\n",
    "    def get_from_db(cls, name):\n",
    "        print(\"find\", name, \"in db\", cls)\n",
    "\n",
    "    @classmethod\n",
    "    def save_to_db(cls, animal):\n",
    "        print(\"save to db\", animal)\n",
    "```\n",
    "\n",
    "\n",
    "## 2. Open Closed Principle\n",
    "\n",
    "\n",
    "### 2.1 Open Closed Principle violation\n",
    "\n",
    "```python\n",
    "def get_animal_sound(animal):\n",
    "    if animal.name == \"lion\":\n",
    "        return \"roar\"\n",
    "    if animal.name == \"cat\":\n",
    "        return \"meow\"\n",
    "```\n",
    "\n",
    "### 2.2 Following the Open Closed Principle\n",
    "\n",
    "```python\n",
    "class Animal:\n",
    "    def __init__(self, name, sound):\n",
    "        self.name = name\n",
    "        self.sound = sound\n",
    "        \n",
    "    def make_sound(self):\n",
    "        print(self.name, \"makes sound\", self.sound)\n",
    "        \n",
    "\n",
    "lion = Animal(\"lion\", \"roar\")\n",
    "cat = Animal(\"cat\", \"meow\")\n",
    "print(lion.sound)\n",
    "# roar\n",
    "lion.make_sound()\n",
    "# lion makes sound roar\n",
    "print(cat.sound)\n",
    "# meow\n",
    "cat.make_sound()\n",
    "# cat makes sound meow\n",
    "```\n",
    "\n",
    "\n",
    "## 3. Liskov Substitution Principle\n",
    "\n",
    "\n",
    "### 3.1 Liskov Substitution Principle violation\n",
    "\n",
    "```python\n",
    "def get_animal_tail_info(animal):\n",
    "    if isinstance(animal, Lion):\n",
    "        return animal.get_lion_tail_info()\n",
    "    if isinstance(animal, Cat):\n",
    "        return animal.get_cat_tail_info()\n",
    "```\n",
    "\n",
    "### 3.2 Following the Liskov Substitution Principle\n",
    "\n",
    "\n",
    "```python\n",
    "class Animal:\n",
    "    def get_tail_info(self):\n",
    "        return \"\"\n",
    "\n",
    "\n",
    "class Lion(Animal):\n",
    "    def get_tail_info(self):\n",
    "        return \"Lion has a big and heavy tail...\"\n",
    "\n",
    "\n",
    "class Cat(Animal):\n",
    "    def get_tail_info(self):\n",
    "        return \"Cat has a nice and furry tail...\"\n",
    "\n",
    "\n",
    "def get_animal_tail_info(animal: Animal):\n",
    "    return animal.get_tail_info()\n",
    "```\n",
    "\n",
    "\n",
    "## 4. Interface Segregation Principle\n",
    "\n",
    "\n",
    "### 4.1 Following the Interface Segregation Principle\n",
    "\n",
    "\n",
    "```python\n",
    "from abc import abstractmethod\n",
    "\n",
    "\n",
    "class MessagingDevice:\n",
    "\n",
    "    @abstractmethod\n",
    "    def send_email(self, recipient, email_object):\n",
    "        pass\n",
    "\n",
    "    @abstractmethod\n",
    "    def send_sms(self, recipient, sms_object):\n",
    "        pass\n",
    "\n",
    "\n",
    "class Smartphone(MessagingDevice):\n",
    "    \"\"\"\n",
    "    Just a regular smartphone\n",
    "    \"\"\"\n",
    "\n",
    "    def send_email(self, recipient, email_object):\n",
    "        print(self, \"send email\", email_object, \"to\", recipient)\n",
    "\n",
    "    def send_sms(self, recipient, sms_object):\n",
    "        print(self, \"send sms\", sms_object, \"to\", recipient)\n",
    "\n",
    "\n",
    "class PDA(MessagingDevice):\n",
    "    \"\"\"\n",
    "    A personal digital assistant (PDA),\n",
    "    also known as a handheld PC\n",
    "    \"\"\"\n",
    "\n",
    "    def send_email(self, recipient, email_object):\n",
    "        print(self, \"send email\", email_object, \"to\", recipient)\n",
    "\n",
    "    def send_sms(self, recipient, sms_object):\n",
    "        print(self, \"send sms\", sms_object, \"to\", recipient)\n",
    "```\n",
    "\n",
    "\n",
    "\n",
    "## 5. Dependency Inversion Principle\n",
    "\n",
    "\n",
    "### 5.1 Dependency Inversion Principle violation\n",
    "\n",
    "```python\n",
    "class LightBulb:\n",
    "    def turn_on(self):\n",
    "        print(\"LightBulb turned on\")\n",
    "\n",
    "    def turn_off(self):\n",
    "        print(\"LightBulb turned off\")\n",
    "\n",
    "\n",
    "class PowerSwitch:\n",
    "    def __init__(self, light_bulb: LightBulb):\n",
    "        self.light_bulb = light_bulb\n",
    "        self.on = False\n",
    "\n",
    "    def toggle(self):\n",
    "        if self.on:\n",
    "            self.light_bulb.turn_off()\n",
    "            self.on = False\n",
    "        else:\n",
    "            self.light_bulb.turn_on()\n",
    "            self.on = True\n",
    "```\n",
    "\n",
    "### 5.2 Following the Dependency Inversion Principle\n",
    "\n",
    "\n",
    "```python\n",
    "\n",
    "# Creating an abstraction\n",
    "\n",
    "from abc import abstractmethod\n",
    "\n",
    "\n",
    "class Switchable:\n",
    "    @abstractmethod\n",
    "    def turn_on(self):\n",
    "        pass\n",
    "\n",
    "    @abstractmethod\n",
    "    def turn_off(self):\n",
    "        pass\n",
    "\n",
    "\n",
    "# Implementing the Switchable interface\n",
    "\n",
    "class LightBulb(Switchable):\n",
    "    def turn_on(self):\n",
    "        print(\"LightBulb turned on\")\n",
    "\n",
    "    def turn_off(self):\n",
    "        print(\"LightBulb turned off\")\n",
    "\n",
    "\n",
    "class PowerSwitch:\n",
    "    def __init__(self, client: Switchable):\n",
    "        if not isinstance(client, Switchable):\n",
    "            raise TypeError(\"expected Switchable, got\", client)\n",
    "\n",
    "        self.client = client\n",
    "        self.on = False\n",
    "\n",
    "    def toggle(self):\n",
    "        if self.on:\n",
    "            self.client.turn_off()\n",
    "            self.on = False\n",
    "        else:\n",
    "            self.client.turn_on()\n",
    "            self.on = True\n",
    "```"
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