AWS Lambda, saving S3 file to /tmp directory - python-3.x

Question

I want to copy a set of files over from S3, and put them in the /tmp directory while my lambda function is running, to use and manipulate the contents. The following code excerpt works fine on my PC (which is running windows)
s3 = boto3.resource('s3')
BUCKET_NAME = 'car_sentiment'
keys = ['automated.csv', 'connected_automated.csv', 'connected.csv',
'summary.csv']
for KEY in keys:
try:
local_file_name = 'tmp/'+KEY
s3.Bucket(BUCKET_NAME).download_file(KEY, local_file_name)
except botocore.exceptions.ClientError as e:
if e.response['Error']['Code'] == "404":
continue
else:
raise
However, when I try to run on AWS lambda, I get:
{
"errorMessage": "[Errno 2] No such file or directory: 'tmp/automated.csv.4Bcd0bB9'",
"errorType": "FileNotFoundError",
"stackTrace": [
[
"/var/task/SentimentForAWS.py",
28,
"my_handler",
"s3.Bucket(BUCKET_NAME).download_file(KEY, local_file_name)"
],
[
"/var/runtime/boto3/s3/inject.py",
246,
"bucket_download_file",
"ExtraArgs=ExtraArgs, Callback=Callback, Config=Config)"
],
[
"/var/runtime/boto3/s3/inject.py",
172,
"download_file",
"extra_args=ExtraArgs, callback=Callback)"
],
[
"/var/runtime/boto3/s3/transfer.py",
307,
"download_file",
"future.result()"
],
[
"/var/runtime/s3transfer/futures.py",
73,
"result",
"return self._coordinator.result()"
],
[
"/var/runtime/s3transfer/futures.py",
233,
"result",
"raise self._exception"
],
[
"/var/runtime/s3transfer/tasks.py",
126,
"__call__",
"return self._execute_main(kwargs)"
],
[
"/var/runtime/s3transfer/tasks.py",
150,
"_execute_main",
"return_value = self._main(**kwargs)"
],
[
"/var/runtime/s3transfer/download.py",
582,
"_main",
"fileobj.seek(offset)"
],
[
"/var/runtime/s3transfer/utils.py",
335,
"seek",
"self._open_if_needed()"
],
[
"/var/runtime/s3transfer/utils.py",
318,
"_open_if_needed",
"self._fileobj = self._open_function(self._filename, self._mode)"
],
[
"/var/runtime/s3transfer/utils.py",
244,
"open",
"return open(filename, mode)"
]
]
}
Why does it think the file name is tmp/automated.csv.4Bcd0bB9 rather than just tmp/automated.csv and how do I fix it? Been pulling my hair out on this one, trying multiple approaches, some of which generate a similar error when running locally on my PC. Thanks!

Answer 1

You should save in /tmp, rather than tmp/.
eg:
local_file_name = '/tmp/' + KEY

Answer 2

Well the reason why lambda gives the above error is because it doesn't allow to write in the heirarchial structure with in the /tmp/ directory. You can write the files directly to /tmp/example.txt dir but not to say /tmp/dir1/example.txt