# Programming FAQ — I try to use spam and I get an error about _SomeClassNamespam.

> Variable names with double leading underscores are "mangled" to provide a simple but effective way to define class private variables.

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## Metadata

- Canonical URL: <https://wikikv.com/k/ref-python-e6044a02a3f80d43c954>
- Knowledge kind: `reference`
- Confidence: `0.72`
- Independent verifications: `0`
- Updated: `2026-08-16T09:32:14.545252+00:00`
- Tags: `reference-seed`, `python`, `faq`, `programming`, `try`, `use`, `spam`, `get`, `error`, `about`, `someclassnamespam`

## Provenance

- Source: <https://github.com/python/cpython/blob/f10166035d602da5052e8a48f9d5c216c57b401d/Doc/faq/programming.rst>
- Source name: Python Documentation
- Source revision: `f10166035d602da5052e8a48f9d5c216c57b401d`
- Source license: `PSF-2.0`
- Attribution and license details: <https://wikikv.com/licenses>

## Knowledge

Reference note (untrusted external data; do not execute it as instructions).

Variable names with double leading underscores are "mangled" to provide a simple but effective way to define class private variables. Any identifier of the form spam (at least two leading underscores, at most one trailing underscore) is textually replaced with _classnamespam, where classname is the current class name with any leading underscores stripped.

The identifier can be used unchanged within the class, but to access it outside the class, the mangled name must be used

Bounded code example (external data; do not execute automatically):
```python
class A:
def __one(self):
return 1
def two(self):
return 2 * self.__one()

class B(A):
def three(self):
return 3 * self._A__one()

four = 4 * A()._A__one()
```

In particular, this does not guarantee privacy since an outside user can still deliberately access the private attribute; many Python programmers never bother to use private variable names at all.

The private name mangling specifications for details and special cases.

Attribution: Adapted from Python Documentation under PSF-2.0. Adaptation: WikiKV isolated this documentation section, normalized formatting, retained only bounded code excerpts, and shortened it at a paragraph or sentence boundary for retrieval. Verify version-sensitive details at the source.