zope.deprecation API

Deprecating objects inside a module

Let’s start with a demonstration of deprecating any name inside a module. To demonstrate the functionality, First, let’s set up an example module containing fixtures we will use:

>>> import os
>>> import tempfile
>>> import zope.deprecation
>>> tmp_d = tempfile.mkdtemp('deprecation')
>>> zope.deprecation.__path__.append(tmp_d)
>>> doctest_ex = '''\
... from . import deprecated
...
... def demo1():
...     return 1
... deprecated('demo1', 'demo1 is no more.')
...
... def demo2():
...     return 2
... deprecated('demo2', 'demo2 is no more.')
...
... def demo3():
...     return 3
... deprecated('demo3', 'demo3 is no more.')
...
... def demo4():
...     return 4
... def deprecatedemo4():
...     """Demonstrate that deprecated() also works in a local scope."""
...     deprecated('demo4', 'demo4 is no more.')
... '''
>>> with open(os.path.join(tmp_d, 'doctest_ex.py'), 'w') as f:
...     _ = f.write(doctest_ex)

The first argument to the deprecated() function is a list of names that should be declared deprecated. If the first argument is a string, it is interpreted as one name. The second argument is the reason the particular name has been deprecated. It is good practice to also list the version in which the name will be removed completely.

Let’s now see how the deprecation warnings are displayed.

>>> import warnings
>>> from zope.deprecation import doctest_ex
>>> with warnings.catch_warnings(record=True) as log:
...     del warnings.filters[:]
...     doctest_ex.demo1()
1
>>> print(log[0].category.__name__)
DeprecationWarning
>>> print(log[0].message)
demo1: demo1 is no more.

>>> import zope.deprecation.doctest_ex
>>> with warnings.catch_warnings(record=True) as log:
...     del warnings.filters[:]
...     zope.deprecation.doctest_ex.demo2()
2
>>> print(log[0].message)
demo2: demo2 is no more.

You can see that merely importing the affected module or one of its parents does not cause a deprecation warning. Only when we try to access the name in the module, we get a deprecation warning. On the other hand, if we import the name directly, the deprecation warning will be raised immediately.

>>> with warnings.catch_warnings(record=True) as log:
...     del warnings.filters[:]
...     from zope.deprecation.doctest_ex import demo3
>>> print(log[0].message)
demo3: demo3 is no more.

Deprecation can also happen inside a function. When we first access demo4, it can be accessed without problems, then we call a function that sets the deprecation message and we get the message upon the next access:

>>> with warnings.catch_warnings(record=True) as log:
...     del warnings.filters[:]
...     doctest_ex.demo4()
4
>>> len(log)
0
>>> doctest_ex.deprecatedemo4()
>>> with warnings.catch_warnings(record=True) as log:
...     del warnings.filters[:]
...     doctest_ex.demo4()
4
>>> print(log[0].message)
demo4: demo4 is no more.

Deprecating methods and properties

New let’s see how properties and methods can be deprecated. We are going to use the same function as before, except that this time, we do not pass in names as first argument, but the method or attribute itself. The function then returns a wrapper that sends out a deprecation warning when the attribute or method is accessed.

>>> from zope.deprecation import deprecation
>>> class MyComponent(object):
...     foo = property(lambda self: 1)
...     foo = deprecation.deprecated(foo, 'foo is no more.')
...
...     bar = 2
...
...     def blah(self):
...         return 3
...     blah = deprecation.deprecated(blah, 'blah() is no more.')
...
...     def splat(self):
...         return 4
...
...     @deprecation.deprecate("clap() is no more.")
...     def clap(self):
...         return 5

And here is the result:

>>> my = MyComponent()
>>> with warnings.catch_warnings(record=True) as log:
...     del warnings.filters[:]
...     my.foo
1
>>> print(log[0].message)
foo is no more.
>>> with warnings.catch_warnings(record=True) as log:
...     del warnings.filters[:]
...     my.bar
2
>>> len(log)
0
>>> with warnings.catch_warnings(record=True) as log:
...     del warnings.filters[:]
...     my.blah()
3
>>> print(log[0].message)
blah() is no more.
>>> with warnings.catch_warnings(record=True) as log:
...     del warnings.filters[:]
...     my.splat()
4
>>> len(log)
0
>>> with warnings.catch_warnings(record=True) as log:
...     del warnings.filters[:]
...     my.clap()
5
>>> print(log[0].message)
clap() is no more.

Deprecating modules

It is also possible to deprecate whole modules. This is useful when creating module aliases for backward compatibility. Let’s imagine, the zope.deprecation module used to be called zope.wanda and we’d like to retain backward compatibility:

>>> import sys
>>> sys.modules['zope.wanda'] = deprecation.deprecated(
...     zope.deprecation, 'A module called Wanda is now zope.deprecation.')

Now we can import wanda, but when accessing things from it, we get our deprecation message as expected:

>>> with warnings.catch_warnings(record=True) as log:
...     del warnings.filters[:]
...     from zope.wanda import deprecated
>>> print(log[0].message)
A module called Wanda is now zope.deprecation.

Before we move on, we should clean up:

>>> del deprecated
>>> del sys.modules['zope.wanda']

Moving modules

When a module is moved, you often want to support importing from the old location for a while, generating a deprecation warning when someone uses the old location. This can be done using the moved function.

To see how this works, we’ll use a helper function to create two fake modules in the zope.deprecation package. First will create a module in the “old” location that used the moved function to indicate the a module on the new location should be used:

>>> import os
>>> created_modules = []
>>> def create_module(modules=(), **kw): #** highlightfail
...     modules = dict(modules)
...     modules.update(kw)
...     for name, src in sorted(modules.items()):
...         pname = name.split('.')
...         if pname[-1] == '__init__':
...             os.mkdir(os.path.join(tmp_d, *pname[:-1])) #* highlightfail
...             name = '.'.join(pname[:-1])
...         with open(os.path.join(tmp_d, *pname) + '.py', 'w') as f:
...             f.write(src) #* hf
...         created_modules.append(name)
...     import importlib
...     if hasattr(importlib, 'invalidate_caches'):
...         importlib.invalidate_caches()
>>> create_module(old_location=
... '''
... import zope.deprecation
... zope.deprecation.moved('zope.deprecation.new_location', 'version 2')
... ''')

and we define the module in the new location:

>>> create_module(new_location=
... '''\
... print("new module imported")
... x = 42
... ''')

Now, if we import the old location, we’ll see the output of importing the old location:

>>> with warnings.catch_warnings(record=True) as log:
...     del warnings.filters[:]
...     import zope.deprecation.old_location
new module imported
>>> print(log[0].message)
... 
zope.deprecation.old_location has moved to zope.deprecation.new_location.
Import of zope.deprecation.old_location will become unsupported
in version 2
>>> zope.deprecation.old_location.x
42

Moving packages

When moving packages, you need to leave placeholders for each module. Let’s look at an example:

>>> create_module({
... 'new_package.__init__': '''\
... print(__name__ + ' imported')
... x=0
... ''',
... 'new_package.m1': '''\
... print(__name__ + ' imported')
... x=1
... ''',
... 'new_package.m2': '''\
... print(__name__ + ' imported')
... def x():
...     pass
... ''',
... 'new_package.m3': '''\
... print(__name__ + ' imported')
... x=3
... ''',
... 'old_package.__init__': '''\
... import zope.deprecation
... zope.deprecation.moved('zope.deprecation.new_package', 'version 2')
... ''',
... 'old_package.m1': '''\
... import zope.deprecation
... zope.deprecation.moved('zope.deprecation.new_package.m1', 'version 2')
... ''',
... 'old_package.m2': '''\
... import zope.deprecation
... zope.deprecation.moved('zope.deprecation.new_package.m2', 'version 2')
... ''',
... })

Now, if we import the old modules, we’ll get warnings:

>>> with warnings.catch_warnings(record=True) as log:
...     del warnings.filters[:]
...     import zope.deprecation.old_package
zope.deprecation.new_package imported
>>> print(log[0].message)
... 
zope.deprecation.old_package has moved to zope.deprecation.new_package.
Import of zope.deprecation.old_package will become unsupported in version 2
>>> zope.deprecation.old_package.x
0

>>> with warnings.catch_warnings(record=True) as log:
...     del warnings.filters[:]
...     import zope.deprecation.old_package.m1
zope.deprecation.new_package.m1 imported
>>> print(log[0].message)
... 
zope.deprecation.old_package.m1 has moved to zope.deprecation.new_package.m1.
Import of zope.deprecation.old_package.m1 will become unsupported in
version 2
>>> zope.deprecation.old_package.m1.x
1

>>> with warnings.catch_warnings(record=True) as log:
...     del warnings.filters[:]
...     import zope.deprecation.old_package.m2
zope.deprecation.new_package.m2 imported
>>> print(log[0].message)
... 
zope.deprecation.old_package.m2 has moved to zope.deprecation.new_package.m2.
Import of zope.deprecation.old_package.m2 will become unsupported in
version 2
>>> zope.deprecation.old_package.m2.x is zope.deprecation.new_package.m2.x
True

>>> (zope.deprecation.old_package.m2.x.__globals__
...  is zope.deprecation.new_package.m2.__dict__)
True

>>> zope.deprecation.old_package.m2.x.__module__
'zope.deprecation.new_package.m2'

We’ll get an error if we try to import m3, because we didn’t create a placeholder for it (Python 3.6 started raising ModuleNotFoundError, a subclass of ImportError with a different error message than earlier releases so we can’t see that directly):

>>> try:
...     import zope.deprecation.old_package.m3
... except ImportError as e:
...    print("No module named" in str(e))
...    print("m3" in str(e))
True
True

Before we move on, let’s clean up the temporary modules / packages:

>>> zope.deprecation.__path__.remove(tmp_d)
>>> import shutil
>>> shutil.rmtree(tmp_d)

Temporarily turning off deprecation warnings

In some cases it is desireable to turn off the deprecation warnings for a short time.

To support such a feature, the zope.deprecation package provides a context manager class, zope.deprecation.Suppressor. Code running inside the scope of a Suppressor will not emit deprecation warnings.

>>> from zope.deprecation import Suppressor
>>> class Foo(object):
...     bar = property(lambda self: 1)
...     bar = deprecation.deprecated(bar, 'bar is no more.')
...     blah = property(lambda self: 1)
...     blah = deprecation.deprecated(blah, 'blah is no more.')
>>> foo = Foo()
>>> with Suppressor():
...    foo.blah
1

Note that no warning is emitted when foo.blah is accessed inside the suppressor’s scope.:

The suppressor is implemented in terms of a __show__ object. One can ask for its status by calling it:

>>> from zope.deprecation import __show__
>>> __show__()
True

Inside a suppressor’s scope, that status is always false:

>>> with Suppressor():
...     __show__()
False

>>> with warnings.catch_warnings(record=True) as log:
...     del warnings.filters[:]
...     foo.bar
1
>>> print(log[0].message)
bar is no more.

If needed, your code can manage the depraction warnings manually using the on() and off() methods of the __show__ object:

>>> __show__.off()
>>> __show__()
False

>>> foo.blah
1

Now, you can also nest several turn-offs, so that calling off() multiple times is meaningful:

>>> __show__.stack
[False]

>>> __show__.off()
>>> __show__.stack
[False, False]

>>> __show__.on()
>>> __show__.stack
[False]
>>> __show__()
False

>>> __show__.on()
>>> __show__.stack
[]
>>> __show__()
True

You can also reset __show__ to True:

>>> __show__.off()
>>> __show__.off()
>>> __show__()
False

>>> __show__.reset()
>>> __show__()
True

Finally, you cannot call on() without having called off() before:

>>> __show__.on()
Traceback (most recent call last):
...
IndexError: pop from empty list