Python Variable Name Converter
snake_case writes hello_world_example. PEP 8 specifies lower_case_with_underscores for functions, variables, methods, modules and packages. Every linter in the Python ecosystem — flake8, pylint, ruff — enforces it by default, and the standard library follows it consistently enough that violating it makes code visibly non-Pythonic.
Conversions
| Input | snake_case |
|---|---|
hello world example | hello_world_example |
XMLHttpRequest | xml_http_request |
user_first_name | user_first_name |
Total Order Count | total_order_count |
XMLHttpRequest becomes xml_http_request. That uniformity is why snake_case survives round-tripping better than the camel family — there is no capitalisation left to get wrong on the way back.The Same Text in Other Cases
| Case | Result |
|---|---|
| camelCase | helloWorldExample |
| PascalCase | HelloWorldExample |
| SCREAMING_SNAKE_CASE | HELLO_WORLD_EXAMPLE |
| kebab-case | hello-world-example |
| Train-Case | Hello-World-Example |
| dot.case | hello.world.example |
PEP 8 Is Enforced by Tooling
Ruff, flake8 and pylint all check naming by default, so a non-conforming name is a CI failure rather than a review comment in most Python projects. The rules extend past variables: modules and packages take short lowercase names, classes are PascalCase, constants are upper case, and a leading underscore marks something internal.
A double leading underscore inside a class triggers name mangling, which is a language feature rather than a style choice — __x becomes _ClassName__x and will not be found by the name you wrote.
Converting in Code
``javascript
const snake = (s) => words(s).map((w) => w.toLowerCase()).join('_');
`
The failure mode is on the way *in*, not out. A converter that splits only on existing underscores turns userId into userid rather than user_id, and the mistake is invisible until someone searches for a column that does not exist.
Converting at the API Boundary
The recurring friction is that JavaScript uses camelCase and Python, Ruby, Go and SQL use
snake_case. The fix is to convert in exactly one place — the client that talks to the API —
rather than letting both conventions into the same codebase.
`javascript
const toCamel = (s) => s.replace(/_([a-z])/g, (_, c) => c.toUpperCase());
const toSnake = (s) => s.replace(/[A-Z]/g, (c) => '_' + c.toLowerCase());
// Recursively, for a whole payload
const convertKeys = (value, fn) =>
Array.isArray(value)
? value.map((v) => convertKeys(v, fn))
: value && typeof value === 'object'
? Object.fromEntries(Object.entries(value).map(([k, v]) => [fn(k), convertKeys(v, fn)]))
: value;
`
Two things to watch: keys that are user data rather than field names must not be
converted, and the round trip is not always lossless — userID → user_id → userId
changes the original.
Where Each Convention Is Mandatory
Not stylistic — these will break if you deviate:
| Context | Requirement |
|---|---|
| Environment variables | Uppercase with underscores; POSIX reserves lowercase |
| Custom HTML elements | Must contain a hyphen |
| Python modules | Cannot contain hyphens; the import statement will not parse |
| SQL identifiers | Folded to one case unless quoted, so camelCase does not survive |
| React components | Must start uppercase, or JSX treats it as an HTML tag |
Renaming Safely
A find-and-replace across a codebase will hit strings, comments and unrelated identifiers.
Use your language server's rename symbol instead — it understands scope. For a bulk rename
across files, restrict the pattern with word boundaries and review the diff before
committing:
`bash
grep -rn '\buserId\b' src/ # look first
``