how to format a python source file with tools?

[李白，字一日]

On Nov 27, 3:35 pm, Ben Finney <ben+pyt... at benfinney.id.au> wrote:
> 李白，字一日 <calid... at gmail.com> writes:
> > or is it possible for large source files?
>
> Is what possible? What do you want the tool to do?
>
> --
>  \           “I do not believe in forgiveness as it is preached by the |
>   `\        church. We do not need the forgiveness of God, but of each |
> _o__)                    other and of ourselves.” —Robert G. Ingersoll |
> Ben Finney

sometimes i need to merge some code snippets from files into a file,
and when time comes to do this merge, i always find it difficult to
reformat the python code
because after pasting and copy, the code indentation different from
one to another.
and it is the tedious job for us to manually move the code from one
segment to another.

so i would like to have a tool to intelligently format the code for me
and make the code more beautiful
and automated.