A language model is a text-to-text function. It has no filesystem handle, no shell, no network socket. Given “explain the code in complex.py”, the only correct response is that it cannot read files.

sequenceDiagram
    participant You
    participant LLM
    You->>LLM: Explain the code in complex.py
    LLM-->>You: No file access — supply the contents

Claude Code is the process that closes that gap. It is an agentic harness: it supplies tools, executes them on the model’s behalf, and drives the model in a loop until the task is done.