### Discussed in https://github.com/apache/airflow/discussions/36076

<div type='discussions-op-text'>

<sup>Originally posted by **timc** December  5, 2023</sup>
### Apache Airflow version

2.7.3

### What happened

When creating a virtual env task and passing in a requirements file like this:

`@task.virtualenv(
            use_dill=True,
            system_site_packages=False,
            requirements='requirements.txt')`

The result is that the contents of the requirements file using to populate the venv is

requirements.txt

Which is wrong. And you get this:

[2023-12-05, 12:33:06 UTC] {{process_utils.py:181}} INFO - Executing cmd: python3 /usr/local/***/.local/lib/python3.10/site-packages/virtualenv /tmp/venv3cdlqjlq
[2023-12-05, 12:33:06 UTC] {{process_utils.py:185}} INFO - Output:
[2023-12-05, 12:33:07 UTC] {{process_utils.py:189}} INFO - created virtual environment CPython3.10.9.final.0-64 in 397ms
[2023-12-05, 12:33:07 UTC] {{process_utils.py:189}} INFO -   creator CPython3Posix(dest=/tmp/venv3cdlqjlq, clear=False, no_vcs_ignore=False, global=False)
[2023-12-05, 12:33:07 UTC] {{process_utils.py:189}} INFO -   seeder FromAppData(download=False, pip=bundle, setuptools=bundle, wheel=bundle, via=copy, app_data_dir=/usr/local/***/.local/share/virtualenv)
[2023-12-05, 12:33:07 UTC] {{process_utils.py:189}} INFO -     added seed packages: pip==23.3.1, setuptools==69.0.2, wheel==0.42.0
[2023-12-05, 12:33:07 UTC] {{process_utils.py:189}} INFO -   activators BashActivator,CShellActivator,FishActivator,NushellActivator,PowerShellActivator,PythonActivator
[2023-12-05, 12:33:07 UTC] {{process_utils.py:181}} INFO - Executing cmd: /tmp/venv3cdlqjlq/bin/pip install -r /tmp/venv3cdlqjlq/requirements.txt
[2023-12-05, 12:33:07 UTC] {{process_utils.py:185}} INFO - Output:
[2023-12-05, 12:33:09 UTC] {{process_utils.py:189}} INFO - ERROR: Could not find a version that satisfies the requirement requirements.txt (from versions: none)
[2023-12-05, 12:33:09 UTC] {{process_utils.py:189}} INFO - HINT: You are attempting to install a package literally named "requirements.txt" (which cannot exist). Consider using the '-r' flag to install the packages listed in requirements.txt
[2023-12-05, 12:33:09 UTC] {{process_utils.py:189}} INFO - ERROR: No matching distribution found for requirements.txt
[2023-12-05, 12:33:09 UTC] {{taskinstance.py:1824}} ERROR - Task failed with exception

The issue appears to be that the requirements parameter is added to a list on construction of the operator so the templating never happens.

### What you think should happen instead

The provided requirements file should be used in the pip command to set up the venv.

### How to reproduce

Create a dag:

```
from datetime import datetime
from airflow.decorators import dag, task

 @dag(schedule_interval=None, start_date=datetime(2021, 1, 1), catchup=False, tags=['example']) 
def virtualenv_task():
    @task.virtualenv(
        use_dill=True,
        system_site_packages=False,
        requirements='requirements.txt',
    )
    def extract():
        import pandas 
        x = pandas.DataFrame()

    extract()

dag = virtualenv_task()
```
And a requirements.txt file

```
pandas
```

Run AirFlow

### Operating System

Ubuntu 23.04

### Versions of Apache Airflow Providers

apache-airflow-providers-amazon==8.2.0
apache-airflow-providers-celery==3.2.1
apache-airflow-providers-common-sql==1.5.2
apache-airflow-providers-ftp==3.4.2
apache-airflow-providers-http==4.4.2
apache-airflow-providers-imap==3.2.2
apache-airflow-providers-postgres==5.5.1
apache-airflow-providers-sqlite==3.4.2

### Deployment

Docker-Compose

### Deployment details

_No response_

### Anything else

Everytime.

### Are you willing to submit PR?

- [ ] Yes I am willing to submit a PR!

### Code of Conduct

- [X] I agree to follow this project's [Code of Conduct](https://github.com/apache/airflow/blob/main/CODE_OF_CONDUCT.md)
</div>
@teardown
        @task.virtualenv
        def f():
            return 1
        with dag_maker() as dag:
            ret = f()
        assert len(dag.task_group.children) == 1
        teardown_task = dag.task_group.children["f"]
        assert teardown_task.is_teardown
        ret.operator.run(start_date=DEFAULT_DATE, end_date=DEFAULT_DATE)
    @pytest.mark.parametrize("on_failure_fail_dagrun", [True, False])
    def test_marking_virtualenv_python_task_as_teardown_with_on_failure_fail(
        self, dag_maker, on_failure_fail_dagrun
    ):
        @teardown(on_failure_fail_dagrun=on_failure_fail_dagrun)
        @task.virtualenv
        def f():
            return 1
        with dag_maker() as dag:
            ret = f()
        assert len(dag.task_group.children) == 1
        teardown_task = dag.task_group.children["f"]
        assert teardown_task.is_teardown
        assert teardown_task.on_failure_fail_dagrun is on_failure_fail_dagrun
        ret.operator.run(start_date=DEFAULT_DATE, end_date=DEFAULT_DATE)