jagged accuracy curve in tensorflow

What is f-string in python

step = 5
test_accuracy = 0.77777
print(f'step {step:05d}, test accuracy {test_accuracy}\n') # f-strings
# It's more simple than
print('step {:05d}, test accuracy {}\n'.format(step, test_accuracy ))

reference

The new f-strings in Python 3.6 | Seasoned & Agile
https://cito.github.io/blog/f-strings/

What’s New In Python 3.6 — Python 3.6.5 documentation
https://docs.python.org/3/whatsnew/3.6.html

PEP 498 – Literal String Interpolation | Python.org
https://www.python.org/dev/peps/pep-0498/