Mock Python's built in print function

Question

I\'ve tried

from mock import Mock
import __builtin__

__builtin__.print = Mock()

But that raises a syntax error. I\'ve also tried patching

Answer 1

If you want to stick with the print statement from 2.x as opposed to the print() function from 2.x, you could mock your sys.stdout instead.

Write a dummy "file", perhaps in about this way:

class Writable(object):
    """Class which has the capability to replace stdout."""
    newwrite = None
    def __init__(self, oldstdout, newwrite=None):
        self.oldstdout = oldstdout
        if newwrite is not None:
            self.newwrite = newwrite
    def write(self, data):
        self.newwrite(self.oldstdout, data)
    @classmethod
    def subclass(cls, writefunc):
        newcls = type('', (cls,),
            dict(write=lambda self, data: writefunc(self.oldstdout, data)
        return newcls

This class expects to be combined with a writing function which gets the printed data. This writing function is supposed to take 2 arguments: the first one with the "old stdout" to be used for printing at the end, and a further one for the data.

Let's take

def mywrite(sink, data):
    sink.write(data.encode("hex"))

for that.

Now you can do

import sys
sys.stdout = Writable(sys.stdout, mywrite)

or you can do

@Writable.subclass
def mywritable(sink, data)
    sink.write(data.encode("hex"))

sys.stdout = mywritable(sys.stdout)

The 2nd version is a bit trickier: it creates a subclass of the Writable with the help of a decorator function which turns the given function into a method of the new class created instead and put into the name where the given function comes from.

After that, you have a new class which can be instantiated with the "old stdout" as argument and can replace sys.stdout after that.