How to use AirFlow to run a folder of python files?

I know you're asking that you "would like to execute those python files (not the Python function through Python Operator)." but I see this as probably using Airflow less effectively than you could be. I also see confusion in the previously written answers so here's the way you wanted, and the way I'd recommend to do the tasks:

Assuming:

dags/
    my_dag_for_task_1_and_2.py
    tasks/
         file1.py
         file2.py

Your request to avoid the PythonOperator:

#  my_dag_for_task_1_and_2.py
import datetime as dt
from airflow import DAG
from airflow.operators import BashOperator

with DAG(
    'my_dag_for_task_1_and_2',
    default_args={
        'owner': 'me',
        'start_date': datetime(…),
        …,
    }, 
    schedule_interval='8 * * * *',
) as dag:
    task_1 = BashOperator(
        task_id='task_1', 
        bash_command='/path/to/python /path/to/dags/tasks/file1.py',
    )
    task_2 = BashOperator(
        task_id='task_2', 
        bash_command='/path/to/python /path/to/dags/tasks/file2.py',
    )
    task_1 >> task_2

You didn't write the Python from scratch for Airflow, but with PythonOperator:

#  my_dag_for_task_1_and_2.py
import datetime as dt
from airflow import DAG
from airflow.operators import PythonOperator
import tasks.file1
import tasks.file2

with DAG(
    'my_dag_for_task_1_and_2',
    default_args={
        'owner': 'me',
        'start_date': datetime(…),
        …,
    }, 
    schedule_interval='8 * * * *',
) as dag:
    task_1 = PythonOperator(
        task_id='task_1', 
        python_callable=file1.function_in_file1,
    )
    task_2 = PythonOperator(
        task_id='task_2', 
        python_callable=file2.function_in_file2,  # maybe main?
    )
    task_1 >> task_2

To execute the python file as a whole, using the BashOperator (As in liferacer's answer):

from airflow.operators.bash_operator import BashOperator

bash_task = BashOperator(
    task_id='bash_task',
    bash_command='python file1.py',
    dag=dag
)

Then, to do it using the PythonOperator call your main function. You should already have a __main__ block, so put what happens in there into a main function, such that your file1.py looks like so:

def main():
    """This gets executed if `python file1` gets called."""
    # my code

if __name__ == '__main__':
    main() 

Then your dag definition:

from airflow.operators.python_operator import PythonOperator

import file1

python_task = PythonOperator(
    task_id='python_task',
    python_callable=file1.main,
    dag=dag
)

You can use BashOperator to execute python files as a task

    from airflow import DAG
    from airflow.operators import BashOperator,PythonOperator
    from datetime import datetime, timedelta

    seven_days_ago = datetime.combine(datetime.today() - timedelta(7),
                                      datetime.min.time())

    default_args = {
        'owner': 'airflow',
        'depends_on_past': False,
        'start_date': seven_days_ago,
        'email': ['[email protected]'],
        'email_on_failure': False,
        'email_on_retry': False,
        'retries': 1,
        'retry_delay': timedelta(minutes=5),
      )

    dag = DAG('simple', default_args=default_args)
t1 = BashOperator(
    task_id='testairflow',
    bash_command='python /home/airflow/airflow/dags/scripts/file1.py',
    dag=dag)