change_dir.py

import os
import contextlib
import boto3

s3 = boto3.client('s3', aws_access_key_id='my_aws_access_key',
                  aws_secret_access_key='my_aws_secret_key',
                  region_name='eu-central-1')


@contextlib.contextmanager
def this_directory(path):
    """
    Change the working dir to the path specified. Then, change back to the original one.
    """
    original_workdir = os.getcwd()
    os.chdir(path)
    try:
        yield
    finally:
        os.chdir(original_workdir)


# Usage:
with this_directory(path='../data'):
    file = 'my_s3_file.csv'
    s3.download_file(bucket='s3_bucket', key=file, filename=file)