decorators in the python standard lib (@deprecated specifically)
PythonDecoratorDeprecatedPython Problem Overview
I need to mark routines as deprecated, but apparently there's no standard library decorator for deprecation. I am aware of recipes for it and the warnings module, but my question is: why is there no standard library decorator for this (common) task ?
Additional question: are there standard decorators in the standard library at all ?
Python Solutions
Solution 1 - Python
Here's some snippet, modified from those cited by Leandro:
import warnings
import functools
def deprecated(func):
"""This is a decorator which can be used to mark functions
as deprecated. It will result in a warning being emitted
when the function is used."""
@functools.wraps(func)
def new_func(*args, **kwargs):
warnings.simplefilter('always', DeprecationWarning) # turn off filter
warnings.warn("Call to deprecated function {}.".format(func.__name__),
category=DeprecationWarning,
stacklevel=2)
warnings.simplefilter('default', DeprecationWarning) # reset filter
return func(*args, **kwargs)
return new_func
# Examples
@deprecated
def some_old_function(x, y):
return x + y
class SomeClass:
@deprecated
def some_old_method(self, x, y):
return x + y
Because in some interpreters the first solution exposed (without filter handling) may result in a warning suppression.
Solution 2 - Python
Here is another solution:
This decorator (a decorator factory in fact) allow you to give a reason message. It is also more useful to help the developer to diagnose the problem by giving the source filename and line number.
EDIT: This code use Zero's recommendation: it replace warnings.warn_explicit
line by warnings.warn(msg, category=DeprecationWarning, stacklevel=2)
,
which prints the function call site rather than the function definition site. It makes debugging easier.
EDIT2: This version allow the developper to specify an optional "reason" message.
import functools
import inspect
import warnings
string_types = (type(b''), type(u''))
def deprecated(reason):
"""
This is a decorator which can be used to mark functions
as deprecated. It will result in a warning being emitted
when the function is used.
"""
if isinstance(reason, string_types):
# The @deprecated is used with a 'reason'.
#
# .. code-block:: python
#
# @deprecated("please, use another function")
# def old_function(x, y):
# pass
def decorator(func1):
if inspect.isclass(func1):
fmt1 = "Call to deprecated class {name} ({reason})."
else:
fmt1 = "Call to deprecated function {name} ({reason})."
@functools.wraps(func1)
def new_func1(*args, **kwargs):
warnings.simplefilter('always', DeprecationWarning)
warnings.warn(
fmt1.format(name=func1.__name__, reason=reason),
category=DeprecationWarning,
stacklevel=2
)
warnings.simplefilter('default', DeprecationWarning)
return func1(*args, **kwargs)
return new_func1
return decorator
elif inspect.isclass(reason) or inspect.isfunction(reason):
# The @deprecated is used without any 'reason'.
#
# .. code-block:: python
#
# @deprecated
# def old_function(x, y):
# pass
func2 = reason
if inspect.isclass(func2):
fmt2 = "Call to deprecated class {name}."
else:
fmt2 = "Call to deprecated function {name}."
@functools.wraps(func2)
def new_func2(*args, **kwargs):
warnings.simplefilter('always', DeprecationWarning)
warnings.warn(
fmt2.format(name=func2.__name__),
category=DeprecationWarning,
stacklevel=2
)
warnings.simplefilter('default', DeprecationWarning)
return func2(*args, **kwargs)
return new_func2
else:
raise TypeError(repr(type(reason)))
You can use this decorator for functions, methods and classes.
Here is a simple example:
@deprecated("use another function")
def some_old_function(x, y):
return x + y
class SomeClass(object):
@deprecated("use another method")
def some_old_method(self, x, y):
return x + y
@deprecated("use another class")
class SomeOldClass(object):
pass
some_old_function(5, 3)
SomeClass().some_old_method(8, 9)
SomeOldClass()
You'll get:
deprecated_example.py:59: DeprecationWarning: Call to deprecated function or method some_old_function (use another function).
some_old_function(5, 3)
deprecated_example.py:60: DeprecationWarning: Call to deprecated function or method some_old_method (use another method).
SomeClass().some_old_method(8, 9)
deprecated_example.py:61: DeprecationWarning: Call to deprecated class SomeOldClass (use another class).
SomeOldClass()
EDIT3: This decorator is now part of the Deprecated library:
New stable release v1.2.13
Solution 3 - Python
As muon suggested, you can install the deprecation
package for this.
> The deprecation
library provides a deprecated
decorator and a fail_if_not_removed
decorator for your tests.
Installation
pip install deprecation
Example Usage
import deprecation
@deprecation.deprecated(deprecated_in="1.0", removed_in="2.0",
current_version=__version__,
details="Use the bar function instead")
def foo():
"""Do some stuff"""
return 1
See http://deprecation.readthedocs.io/ for the full documentation.
Solution 4 - Python
I guess the reason is that Python code can't be processed statically (as it done for C++ compilers), you can't get warning about using some things before actually using it. I don't think that it's a good idea to spam user of your script with a bunch of messages "Warning: this developer of this script is using deprecated API".
Update: but you can create decorator which will transform original function into another. New function will mark/check switch telling that this function was called already and will show message only on turning switch into on state. And/or at exit it may print list of all deprecated functions used in program.
Solution 5 - Python
You can create a utils file
import warnings
def deprecated(message):
def deprecated_decorator(func):
def deprecated_func(*args, **kwargs):
warnings.warn("{} is a deprecated function. {}".format(func.__name__, message),
category=DeprecationWarning,
stacklevel=2)
warnings.simplefilter('default', DeprecationWarning)
return func(*args, **kwargs)
return deprecated_func
return deprecated_decorator
And then import the deprecation decorator as follows:
from .utils import deprecated
@deprecated("Use method yyy instead")
def some_method()"
pass
Solution 6 - Python
UPDATE: I think is better, when we show DeprecationWarning only first time for each code line and when we can send some message:
import inspect
import traceback
import warnings
import functools
import time
def deprecated(message: str = ''):
"""
This is a decorator which can be used to mark functions
as deprecated. It will result in a warning being emitted
when the function is used first time and filter is set for show DeprecationWarning.
"""
def decorator_wrapper(func):
@functools.wraps(func)
def function_wrapper(*args, **kwargs):
current_call_source = '|'.join(traceback.format_stack(inspect.currentframe()))
if current_call_source not in function_wrapper.last_call_source:
warnings.warn("Function {} is now deprecated! {}".format(func.__name__, message),
category=DeprecationWarning, stacklevel=2)
function_wrapper.last_call_source.add(current_call_source)
return func(*args, **kwargs)
function_wrapper.last_call_source = set()
return function_wrapper
return decorator_wrapper
@deprecated('You must use my_func2!')
def my_func():
time.sleep(.1)
print('aaa')
time.sleep(.1)
def my_func2():
print('bbb')
warnings.simplefilter('always', DeprecationWarning) # turn off filter
print('before cycle')
for i in range(5):
my_func()
print('after cycle')
my_func()
my_func()
my_func()
Result:
before cycle
C:/Users/adr-0/OneDrive/Projects/Python/test/unit1.py:45: DeprecationWarning: Function my_func is now deprecated! You must use my_func2!
aaa
aaa
aaa
aaa
aaa
after cycle
C:/Users/adr-0/OneDrive/Projects/Python/test/unit1.py:47: DeprecationWarning: Function my_func is now deprecated! You must use my_func2!
aaa
C:/Users/adr-0/OneDrive/Projects/Python/test/unit1.py:48: DeprecationWarning: Function my_func is now deprecated! You must use my_func2!
aaa
C:/Users/adr-0/OneDrive/Projects/Python/test/unit1.py:49: DeprecationWarning: Function my_func is now deprecated! You must use my_func2!
aaa
Process finished with exit code 0
We can just click on the warning path and go to the line in PyCharm.
Solution 7 - Python
Python
is a dynamically typed language. Not necessary declare the type to variable or argument type for function statically.
Since its dynamic every thing if processed at runtime. Even if a method is deprecated it will be known at runtime or during interpretation only.
use deprecation module to deprecate methods.
> deprecation is a library that enables automated deprecations. It > offers the deprecated() decorator to wrap functions, providing proper > warnings both in documentation and via Python’s warnings system, as > well as the deprecation.fail_if_not_removed() decorator for test > methods to ensure that deprecated code is eventually removed.
Installing :
python3.10 -m pip install deprecation
Small demonstration:
import deprecation
@deprecation.deprecated(details="Use bar instead")
def foo():
print("Foo")
def bar():
print("Bar")
foo()
bar()
Output:
test.py: DeprecatedWarning: foo is deprecated. Use bar instead
foo()
Foo
Bar