How do names, objects, and assignment work in Python?

Explains Python assignment as name binding and connects identity, type, value, aliasing, mutation, and rebinding.

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TL;DR

In Python, values are objects and a name refers to an object. Assignment binds or rebinds a name; it does not declare a fixed type for that name and it does not copy the object. After second = first, both names refer to the same object until one name is rebound. Every object has an identity, a type, and a value. Whether shared references are observable depends on the object: mutating a shared list is visible through both names, while an operation on an integer produces another object and rebinds a name.

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A correct mental model of Python values that can explain later behavior around arguments, collections, defaults, and equality.

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Overview
Python code becomes much easier to reason about once assignment is understood as binding a name to an object rather than copying a value into a typed box.
In Python, values are objects and a name refers to an object. Assignment binds or rebinds a name; it does not declare a fixed type for that name and it does not copy the object. After second = first, both names refer to the same object until one name is rebound. Every object has an identity, a type, and a value. Whether shared references are observable depends on the object: mutating a shared list is visible through both names, while an operation on an integer produces another object and rebinds a name.
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This model separates rebinding from mutation. If orders and refer to one list, changes that list, so sees the new item. If runs instead, only the name is rebound; the original list is unchanged. Function parameters, attributes, collection elements, and imported names all participate in binding. Type annotations can describe intended bindings for tools, but the runtime name can still be rebound unless application logic prevents it.

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Details

Saying a Python variable contains an object in a fixed typed box.
Assuming assignment automatically copies a list or dictionary.
Using rebinding and mutation as interchangeable terms.
Explaining language semantics only through CPython memory addresses.

How do names, objects, and assignment work in Python?

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