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The SemanticRouter is the main class of the semantic router. It is responsible for making decisions about which route to take based on an input utterance. A SemanticRouter consists of an encoder, an index, and a list of routes. Route layers that include dynamic routes (i.e. routes that can generate dynamic decision outputs) also include an llm. To use a SemanticRouter we first need some routes. We can initialize them like so: 
from semantic_router import Route

politics = Route(
    name="politics",
    utterances=[
        "isn't politics the best thing ever",
        "why don't you tell me about your political opinions",
        "don't you just love the president",
        "don't you just hate the president",
        "they're going to destroy this country!",
        "they will save the country!",
    ],
)

chitchat = Route(
    name="chitchat",
    utterances=[
        "how's the weather today?",
        "how are things going?",
        "lovely weather today",
        "the weather is horrendous",
        "let's go to the chippy",
    ],
)
We initialize an encoder — there are many options available here, from local to API-based. For now we’ll use the OpenAIEncoder. 
import os
from semantic_router.encoders import OpenAIEncoder

os.environ["OPENAI_API_KEY"] = "<YOUR_API_KEY>"

encoder = OpenAIEncoder()
Now we define the RouteLayer. When called, the route layer will consume text (a query) and output the category (Route) it belongs to — to initialize a RouteLayer we need our encoder model and a list of routes. 
from semantic_router import SemanticRouter

sr = SemanticRouter(encoder=encoder, routes=routes, auto_sync="local")
Now we can call the RouteLayer with an input query: 
sr("don't you love politics?")

[Out]: RouteChoice(name='politics', function_call=None, similarity_score=None)
The output is a RouteChoice object, which contains the name of the route, the function call (if any), and the similarity score that triggered the route choice. We can try another query: 
sr("how's the weather today?")

[Out]: RouteChoice(name='chitchat', function_call=None, similarity_score=None)
Both are classified accurately, what if we send a query that is unrelated to our existing Route objects? 
sr("I'm interested in learning about llama 3")

[Out]: RouteChoice(name=None, function_call=None, similarity_score=None)
In this case, the RouteLayer is unable to find a route that matches the input query and so returns a RouteChoice with name=None. We can also retrieve multiple routes with their associated score using retrieve_multiple_routes: 
sr.retrieve_multiple_routes("Hi! How are you doing in politics??")

[Out]: [RouteChoice(name='politics', function_call=None, similarity_score=0.859),
        RouteChoice(name='chitchat', function_call=None, similarity_score=0.835)]
If retrieve_multiple_routes is called with a query that does not match any routes, it will return an empty list: 
sr.retrieve_multiple_routes("I'm interested in learning about llama 3")

[Out]: []
You can find an introductory notebook for the route layer here.