python: ignoring leading ">>>" and "..." in interactive mode?

IPython will do this for you automatically.

In [5]: >>> print("hello")
hello

In [10]: >>> print(
   ....: ... "hello"
   ....: )
hello

Not quite the same as pasting into the shell, but the doctest module can be useful. It scans a python module or regular text file looking for interactive script fragments and then runs them. Its primary use case is to blend documentation and unit test. Suppose you have a tutorial such as

This is some code to demonstrate the power of the `if`
statement. 

>>> if True:
...     print("x")
... 
x

Remember, each `if` increases entropy in the universe,
so use with care.

>>> if False:
...     print("y")
... 

Save it to a file and then run doctest

$ python -m doctest -v k.txt
Trying:
    if True:
        print("x")
Expecting:
    x
ok
Trying:
    if False:
        print("y")
Expecting nothing
ok
1 items passed all tests:
   2 tests in k.txt
2 tests in 1 items.
2 passed and 0 failed.
Test passed.

doctest runs the script fragments and compares it to the expected output.

UPDATE

Here's a script that will take what's in the clipboard and paste back the python script fragments. Copy your example, run this script and then paste into the shell.

#!/usr/bin/env python3

import os
import pyperclip

pyperclip.copy(os.linesep.join(line[4:] 
    for line in pyperclip.paste().split(os.linesep)
    if line[:4] in ('>>> ', '... ')))