Set a Read-Only Attribute in Python?

Question

Given how dynamic Python is, I\'ll be shocked if this isn\'t somehow possible:

I would like to change the implementation of sys.stdout.write.

I

Answer 1

Despite Python mostly being a dynamic language, there are native objects types like str, file (including stdout), dict, and list that are actually implemented in low-level C and are completely static:

>>> a = []
>>> a.append = 'something else'
Traceback (most recent call last):
  File "", line 1, in 
AttributeError: 'list' object attribute 'append' is read-only

>>> a.hello = 3
Traceback (most recent call last):
  File "", line 1, in 
AttributeError: 'list' object has no attribute 'hello'

>>> a.__dict__  # normal python classes would have this
Traceback (most recent call last):
  File "", line 1, in 
AttributeError: 'list' object has no attribute '__dict__'

If your object is native C code, your only hope is to use an actual regular class. For your case, like already mentioned, you could do something like:

class NewOut(type(sys.stdout)):
    def write(self, *args, **kwargs):
        super(NewOut, self).write('The new one was called! ')
        super(NewOut, self).write(*args, **kwargs)
sys.stdout = NewOut()

or, to do something similar to your original code:

original_stdoutWrite = sys.stdout.write
class MyClass(object):
    pass
sys.stdout = MyClass()
def new_stdoutWrite(*a, **kw):
    original_stdoutWrite("The new one was called! ")
    original_stdoutWrite(*a, **kw)
sys.stdout.write = new_stdoutWrite