python-pep8

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# PEP 8 for Python

A summary of [PEP 8](https://peps.python.org/pep-0008/) with practical do/don't examples. Ruff/black handle formatting automatically — this guide is about the *semantic* decisions auto-formatters do not make.

## 1. Code layout

### Indentation

4 spaces per level. No tabs in new code.

```python
# OK
def f(
        a, b, c,
        d):
    print(a)

# OK (vertical alignment)
result = some_fn(arg1, arg2,
                 arg3, arg4)
```

### Line length

- Code: **79** characters (PEP 8) or **88** (black/ruff default — recommended).
- Docstrings/comments: **72**.

```python
# Bad (too long)
result = some_very_long_function_name_that_exceeds_the_character_limit(a, b, c)

# Good
result = some_very_long_function_name_that_exceeds_the_character_limit(
    a, b, c,
)
```

### Blank lines

- **Two** blank lines between top-level functions/classes.
- **One** between methods of a class.
- Blank lines inside a function — sparingly, for logical blocks.

```python
class A:
    def m1(self): ...

    def m2(self): ...


def standalone():
    ...
```

### Line breaks at binary operators

Break **before** the operator, not after (mathematical convention, reads more clearly).

```python
# Good
income = (gross_wages
          + taxable_interest
          - ira_deduction)

# Bad
income = (gross_wages +
          taxable_interest -
          ira_deduction)
```

### Encoding

UTF-8 without BOM. No `# -*- coding: utf-8 -*-` in Python 3 (it is already the default).

## 2. Imports

Groups (with a blank line between):
1. Standard library.
2. Third-party packages.
3. Local modules.

```python
import os
import sys
from datetime import datetime

import flask
import peewee

from models import User
from serializers import user_serializer
```

- **One import per line**: `import os` + `import sys`, not `import os, sys`.
- **Absolute imports preferred**: `from myapp.utils import x`, not `from .utils import x` (except in explicit package cases).
- **No** `from x import *`.
- Imports at the top of the file, after the module docstring.

## 3. Naming

| Entity | Style | Example |
|---|---|---|
| Module / package | `snake_case` | `data_processor.py` |
| Class | `PascalCase` | `UserAccount`, `HTTPServer` |
| Exception | `PascalCase` + `Error` | `ValidationError` |
| Function, method | `snake_case` | `calculate_total` |
| Variable | `snake_case` | `user_count` |
| Constant | `UPPER_CASE` | `MAX_CONNECTIONS = 100` |
| Type variable | short `PascalCase` | `T`, `KT`, `VT` |

Special notes:

- `self` for instance methods, `cls` for classmethod. Not `this`, not `obj`.
- Conflict with a keyword: `class_`, `type_` (trailing underscore).
- **One** leading `_` — non-public (by convention, not enforced).
- **Two** leading `__` — name mangling (only meaningful in inheritance).
- **Two** on both sides `__name__` — dunder, do not define your own.

```python

From wachawo/claude-skills, MIT.

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