I did, it is not string. Why?

yes!

You got advantage of dictionary duplicate updation behaviour .. good one

It is a switch to encode or decode your text: 1 for encoding, -1 for decoding.

What is mode in function caeser_cipher?

did you print that string, to see what it is?

No, the expected value was 'foobar002' in that case. 'foobar0011' was the wrong returned value. The input was 'foobar001'

I pass all the tests and attempts but at the end it gives the error as below:

increment_string
str4=int(newL)
ValueError: invalid literal for int() with base 10:

here newL is string, while converting to intger I am getting this traceback.
Please someone help me out...........

I am also getting same valueerror for below line:
increment_string
str4=int(str(newL))
ValueError: invalid literal for int() with base 10:

I am also getting same error:
increment_string
str4=int(str(newL))
ValueError: invalid literal for int() with base 10:

Please someone help me

No it should return foobar0012