Create chapter15.md

chapter15.md

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+## Chapter 15: LangChain Best Practices and Optimization
+We will introduce best practices for using LangChain effectively and techniques for optimizing performance.
+
+```
+from langchain.llms import OpenAI
+from langchain.prompts import PromptTemplate
+from langchain.chains import LLMChain
+from langchain.cache import InMemoryCache
+import langchain
+import time
+
+# 
+langchain.llm_cache = InMemoryCache()
+
+# LLM
+llm = OpenAI(temperature=0.1)
+
+#
+template = """
+You are an AI assistant specialized in {topic}.
+Please provide a concise answer to the following question:
+Question: {question}
+Answer:
+"""
+
+prompt = PromptTemplate(
+    input_variables=["topic", "question"],
+    template=template
+)
+
+# 
+chain = LLMChain(llm=llm, prompt=prompt)
+
+# 
+start_time = time.time()
+
+# 
+for _ in range(5):
+    response = chain.run(topic="Python programming", question="What is a list comprehension?")
+    print(response)
+
+end_time = time.time()
+print(f"Execution time: {end_time - start_time} seconds")
+
+# 
+try:
+    invalid_response = chain.run(topic="Invalid topic", question="This will cause an error")
+except Exception as e:
+    print(f"An error occurred: {e}")
+    
+
+# 
+del llm
+del chain
+
+```