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以下内容来自chatGPT的回答（正解，已验证）
问题1：how to use --extra-index-url in requirements.txt in python?
To use `--extra-index-url` in `requirements.txt` in Python, you need to follow these steps:
1. Open `requirements.txt` in a text editor.
2. Add the `--extra-index-url` option followed by the URL of the extra index you want to use. Separate multiple URLs with commas.
Example:
```
--extra-index-url https://custom.internal.pypi.org/simple/
```
3. Add the package(s) you want to install from the extra index.
Example:
```
requests==2.25.1
custom-package==1.0.0
```
4. Save the `requirements.txt` file.
5. Install the packages using `pip` and include the `--extra-index-url` option.
Example:
```
pip install -r requirements.txt --extra-index-url https://custom.internal.pypi.org/simple/
```
This will install the packages from both the default index and the extra index specified in the `requirements.txt` file.
问题2：how to use multiple --extra-index-url in requirements.txt in python?
You can use multiple `--extra-index-url` options in your `requirements.txt` file by specifying each URL separated by a space. Example:
--extra-index-url URL1 --extra-index-url URL2
In this example, `URL1` and `URL2` should be replaced with the actual URLs you want to use as extra index URLs for package installation.
Here's an example of `requirements.txt` file that uses multiple extra index URLs:
--extra-index-url https://pypi.org/simple
--extra-index-url https://some.custom.repo/simple
package1==1.0.0
package2==2.0.0
In this example, the `package1` and `package2` packages will be installed from either the default PyPI repository or the `some.custom.repo` repository depending on their availability.