Dspy Fundamentals

DSPy Fundamentals (3.2.x)

DSPy is the "PyTorch for prompts" — you declare Signatures (typed I/O contracts), compose them into Modules, and let optimizers (not you) tune the instructions and few-shot examples. Never write raw prompts.

The one-paragraph model

Configure a single LM globally with dspy.configure(lm=...). Define a dspy.Signature subclass with dspy.InputField() / dspy.OutputField() (docstring becomes the instruction). Wrap it in a predictor — dspy.Predict (direct), dspy.ChainOfThought (adds reasoning), dspy.ReAct (tool-using agent), dspy.ProgramOfThought (code-executing), or dspy.RLM (long-context). Subclass dspy.Module to compose multi-step programs. For built-in providers, use dspy.LM("provider/model"); for a truly custom backend, subclass dspy.BaseLM. Optimize later with GEPA.

Canonical template

import dspy

dspy.configure(lm=dspy.LM("openai/gpt-4o"), track_usage=True)

class QuestionAnswer(dspy.Signature):
    """Answer questions with rigorous step-by-step reasoning."""
    question: str = dspy.InputField()
    answer: str = dspy.OutputField(desc="concise final answer")