# python: String Translation Patterns
URL: https://generaltranslation.com/en-US/docs/python/guides/strings.mdx
---
title: String Translation Patterns
description: Translating strings in Python with t(), msg(), variables, and derive()
---

There are two ways to translate strings in GT's Python libraries:

1. **Inline with `t()`** — translate strings directly in your route handlers
2. **Pre-registered with `msg()`** — define strings at module scope, resolve at runtime

## Inline translation with `t()`

Use [`t()`](/docs/python/api/t) to translate a string in the current request's locale:

<Tabs items={['Flask', 'FastAPI']}>
  <Tab value="Flask">
  ```python
  from gt_flask import t

  @app.route('/api/greeting')
  def greeting():
      return { 'message': t('Hello, world!') }
  ```
  </Tab>
  <Tab value="FastAPI">
  ```python
  from gt_fastapi import t

  @app.get('/api/greeting')
  def greeting():
      return { 'message': t('Hello, world!') }
  ```
  </Tab>
</Tabs>

## Pre-registered strings with `msg()`

Use [`msg()`](/docs/python/api/t) to register strings at module scope, then call them in handlers:

```python title="messages.py"
from gt_flask import msg  # or gt_fastapi

GREETING = msg('Hello, world!')
WELCOME = msg('Welcome, {name}!')
NOT_FOUND = msg('Resource not found.')
```

```python title="routes.py"
from messages import GREETING, WELCOME, NOT_FOUND

@app.route('/api/greeting')
def greeting():
    return {
        'greeting': GREETING(),
        'welcome': WELCOME(name='Alice'),
    }

@app.errorhandler(404)
def not_found(e):
    return { 'error': NOT_FOUND() }, 404
```

<Callout>
  Both `t()` and `msg()` produce identical translations. Use `msg()` when the same string appears in multiple places or when you want all strings in one file.
</Callout>

## Variable interpolation

### With `t()`

Use `{name}` placeholders and pass values as keyword arguments:

```python
t('Welcome, {name}!', name=user.display_name)
t('You have {count} new messages.', count=unread_count)
```

### With `declare_var()` and `decode_vars()`

For more control over variable handling, use [`declare_var()`](/docs/python/api/declare-var) and [`decode_vars()`](/docs/python/api/decode-vars):

```python
from gt_flask import declare_var, decode_vars

template = t('Hello, {name}! You have {count} items.')
result = decode_vars(template, {
    'name': declare_var('name', 'Guest'),
    'count': declare_var('count', 0),
})
```

## Using `derive()` for word agreement

[`derive()`](/docs/python/api/derive) generates grammatically correct variants — useful for languages where words change form based on context (gender, number, case):

```python
from gt_flask import t, derive

count = 3
item_word = derive('item', {'one': 'item', 'other': 'items'})
message = t('You have {count} {item}.', count=count, item=item_word)
```

See the [derive tutorial](/docs/python/tutorials/derive) for more patterns.

## Using `$context` for disambiguation

Ambiguous strings can produce inaccurate translations. Add `$context` to guide the translator:

```python
t('Apple', context='the technology company')
t('Spring', context='the season, not a coil')
t('Bank', context='a financial institution')

# Also works with msg()
APPLE = msg('Apple', context='the fruit')
```

## Next steps

- [`t()` API reference](/docs/python/api/t)
- [`declare_var()` API reference](/docs/python/api/declare-var)
- [`derive()` API reference](/docs/python/api/derive)
- [Locale Detection & Middleware](/docs/python/guides/middleware) — how locale context works