Writing a list to a txt file with Python and AWS lambda

Question

I am developing a lambda function that needs to write each element of a list 'my_list', in a line of my 'upload.txt' file.

I have used the next code :

my_list=['hello', 'world', 'good', 'morning']
with open("upload.txt", "w+") as a_file:
   for item in my_list:
       a_file.write("%s\n" % item)
   file_dict = {"upload.txt": a_file}
   response = requests.post(url, files=file_dict)

When I try to test my lambda it gave me the next error:

"errorMessage": "[Errno 30] Read-only file system: 'upload.txt'",
"errorType": "OSError",

It is strange because I will create that file now so why it is written read only file

Does this answer your question? Error "Read-only file system" in AWS Lambda when downloading a file from S3 — Ermiya Eskandary
– Ermiya Eskandary, Commented Jun 8, 2022 at 10:51

Marek Knappe · Accepted Answer · 2022-06-08 09:13:23Z

1

It actually doesn't allow you to write it; just use /tmp/ directory to write temporary files for lambda. Just remember the files in /tmp are not always cleaned in concurrent run of lambdas.

answered Jun 8, 2022 at 9:13

Marek Knappe

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2 Comments

baddy Over a year ago

means I need to add ´/tmp/´ to ´upload.txt´ path? it is strange because if I used only one element to write in this file it works fine but a list with many elements no

Marek Knappe Over a year ago

yes, just instead of upload.txt - use /tmp/upload.txt in both places

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