# python: initialize_gt
URL: https://generaltranslation.com/en-US/docs/python/api/initialize-gt.mdx
---
title: initialize_gt
description: API reference for the initialize_gt setup function
---

## Overview

The `initialize_gt` function configures General Translation for a Flask or FastAPI app.
It must be called once before any translation functions are used.

Settings are automatically loaded from a `gt.config.json` file in the current working directory.
Any keyword arguments override the config file values.

<Tabs items={['Flask', 'FastAPI']}>
  <Tab value="Flask">
  ```python
  from flask import Flask
  from gt_flask import initialize_gt

  app = Flask(__name__)
  initialize_gt(app)
  ```
  </Tab>
  <Tab value="FastAPI">
  ```python
  from fastapi import FastAPI
  from gt_fastapi import initialize_gt

  app = FastAPI()
  initialize_gt(app)
  ```
  </Tab>
</Tabs>

## Reference

### Parameters

<TypeTable
  type={{
    "app": {
      type: 'Flask | FastAPI',
      description: 'The application instance.',
    },
    "default_locale?": {
      type: 'str',
      optional: true,
      description: 'Source locale. Defaults to config file value or "en".',
    },
    "locales?": {
      type: 'list[str]',
      optional: true,
      description: 'Target locales to support.',
    },
    "custom_mapping?": {
      type: 'CustomMapping',
      optional: true,
      description: 'Custom locale mapping.',
    },
    "project_id?": {
      type: 'str',
      optional: true,
      description: 'GT project ID for CDN translation loading.',
    },
    "cache_url?": {
      type: 'str',
      optional: true,
      description: 'CDN base URL override.',
    },
    "get_locale?": {
      type: '(request) -> str',
      optional: true,
      description: 'Custom locale detection callback. Defaults to parsing the Accept-Language header.',
    },
    "load_translations?": {
      type: '(locale: str) -> dict[str, str]',
      optional: true,
      description: 'Custom function to load translations for a locale.',
    },
    "eager_loading?": {
      type: 'bool',
      optional: true,
      default: 'True',
      description: 'Load all translations at startup.',
    },
    "config_path?": {
      type: 'str',
      optional: true,
      description: 'Path to a gt.config.json file. Defaults to "gt.config.json" in the CWD.',
    },
    "load_config?": {
      type: '(path: str | None) -> GTConfig',
      optional: true,
      description: 'Custom config loader replacing the default.',
    },
  }}
/>

### Returns

`I18nManager` — the configured translation manager instance.

---

## Config file

Create a `gt.config.json` in your project root. All fields are optional:

```json title="gt.config.json"
{
  "projectId": "your-project-id",
  "defaultLocale": "en",
  "locales": ["es", "fr"],
  "cacheUrl": "https://custom-cache.example.com"
}
```

Settings from `gt.config.json` are used as defaults. Any keyword arguments passed to `initialize_gt` take precedence.

---

## Examples

### Minimal setup (with config file)

```python
from flask import Flask
from gt_flask import initialize_gt

app = Flask(__name__)
initialize_gt(app)
```

### With custom translation loader

```python
from flask import Flask
from gt_flask import initialize_gt

app = Flask(__name__)

def load_translations(locale: str) -> dict[str, str]:
    # Load translations from your own source
    ...

initialize_gt(app, load_translations=load_translations)
```

### With custom locale detection

```python
from flask import Flask
from gt_flask import initialize_gt

app = Flask(__name__)

def get_locale(request):
    return request.args.get("lang", "en")

initialize_gt(app, get_locale=get_locale)
```

---

## Notes

- `initialize_gt` must be called **once** before using `t` or any other translation function.
- On Flask, it registers a `before_request` hook for locale detection.
- On FastAPI, it registers middleware for locale detection and wraps the app lifespan for eager loading.