Code blocks (#11648)

* Run black on Python code blocks, syntax fixes

https://github.com/scop/misc/blob/master/black_markdown.py

* Code block language marker fixes

* String formatting style tweaks

source/_cookbook/python_component_mqtt_basic.markdown

@@ -18,21 +18,21 @@ This example follows a topic on MQTT and updates the state of an entity to the l
 import homeassistant.loader as loader
 
 # The domain of your component. Should be equal to the name of your component.
-DOMAIN = 'hello_mqtt'
+DOMAIN = "hello_mqtt"
 
 # List of integration names (string) your integration depends upon.
-DEPENDENCIES = ['mqtt']
+DEPENDENCIES = ["mqtt"]
 
 
-CONF_TOPIC = 'topic'
-DEFAULT_TOPIC = 'home-assistant/hello_mqtt'
+CONF_TOPIC = "topic"
+DEFAULT_TOPIC = "home-assistant/hello_mqtt"
 
 
 def setup(hass, config):
     """Set up the Hello MQTT component."""
     mqtt = hass.components.mqtt
     topic = config[DOMAIN].get(CONF_TOPIC, DEFAULT_TOPIC)
-    entity_id = 'hello_mqtt.last_message'
+    entity_id = "hello_mqtt.last_message"
 
     # Listener to be called when we receive a message.
     # The msg parameter is a Message object with the following members:
@@ -45,15 +45,15 @@ def setup(hass, config):
     mqtt.subscribe(topic, message_received)
 
     # Set the initial state.
-    hass.states.set(entity_id, 'No messages')
+    hass.states.set(entity_id, "No messages")
 
     # Service to publish a message on MQTT.
     def set_state_service(call):
         """Service to send a message."""
-        mqtt.publish(topic, call.data.get('new_state'))
+        mqtt.publish(topic, call.data.get("new_state"))
 
     # Register our service with Home Assistant.
-    hass.services.register(DOMAIN, 'set_state', set_state_service)
+    hass.services.register(DOMAIN, "set_state", set_state_service)
 
     # Return boolean to indicate that initialization was successfully.
     return True