What do >> and << mean in Python?

Question

I notice that I can do things like 2 << 5 to get 64 and 1000 >> 2 to get 250.

Also I can use >> in print:

print >>obj, "Hello world"

What is happening here?

Answer 1

The >> operator in your example is used for two different purposes. In C++ terms, this operator is overloaded. In the first example, it is used as a bitwise operator (right shift),

2 << 5  # shift left by 5 bits
        # 0b10 -> 0b1000000
1000 >> 2  # shift right by 2 bits
           # 0b1111101000 -> 0b11111010

While in the second scenario it is used for output redirection. You use it with file objects, like this example:

with open('foo.txt', 'w') as f:
    print >>f, 'Hello world'  # "Hello world" now saved in foo.txt

This second use of >> only worked on Python 2. On Python 3 it is possible to redirect the output of print() using the file= argument:

with open('foo.txt', 'w') as f:
    print('Hello world', file=f)  # "Hello world" now saved in foo.txt

Answer 2

These are bitwise shift operators.

Quoting from the docs:

x << y

Returns x with the bits shifted to the left by y places (and new bits on the right-hand-side are zeros). This is the same as multiplying x by 2**y.

x >> y

Returns x with the bits shifted to the right by y places. This is the same as dividing x by 2**y.