How do I print double in Python with exact precision?

I need to print double with precision equal exactly to 6, I found function round:

print(str(round(result, 6))

But in case result itself has less precision, the print function skips zeros at the end.

Gor example, the output of such code,

print(str(round(4.0, 6)))

is

4.0

But what I need is

4.000000

How can I reach this?