What does "print >>" do in python?

The >> sys.stderr part makes the print statement output to stderr instead of stdout in Python 2.

To quote the documentation:

print also has an extended form, defined by the second portion of the syntax described above. This form is sometimes referred to as “print chevron.” In this form, the first expression after the >> must evaluate to a “file-like” object, specifically an object that has a write() method as described above. With this extended form, the subsequent expressions are printed to this file object. If the first expression evaluates to None, then sys.stdout is used as the file for output.

In Python 3 use the file argument to the print() function:

 print("spam", file=sys.stderr)

To convert these from Python 2 to Python 3, change:

print >>sys.stderr, 'Hello'

to:

print('Hello', file=sys.stderr)