The Python Execution Model Explained Through Code Tracing

Short summary

When you run Python code, the interpreter compiles it to bytecode and manages name references through namespace dictionaries tied to stack frames for each function call. Understanding how mutation works—the difference between operations that modify existing objects versus those that create new ones—is fundamental to predicting behavior in unfamiliar situations and debugging effectively. This explanation uses code tracing to reveal what's actually happening under the hood, converting confusing surprises into predictable patterns.

• •Python names are references to objects stored in namespace dictionaries, not value containers
• •Each function call creates a stack frame with its own local namespace that disappears when the function returns
• •Mutation-related surprises stem from whether an operation creates a new object or modifies an existing one

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