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# The decorator module is alive and kicking
+++
Have you ever heard of the decorator module?
+++
Have you ever heard of IPython?
+++
Every time you fire an IPython instance you are importing
the decorator module :-)
+++
Several frameworks and tools depend on it, so it is one of the most
downloaded packages on PyPI
+++
**Famous last words**
decorator 0.1, May 2005: *this is a hack, surely they will fix the signature
in the next release of Python*
...
+++
# or maybe not
+++?image=releases.png
+++
**It is joy to maintain**
- next to zero bugs
- I get very few questions
- I usually implement something new only when there is new Python release
---
The recommended way to write decorators in Python
```python
from functools import wraps
def trace(f):
@wraps(f)
def wrapper(*args, **kwds):
print('Calling', f.__name__)
return f(*args, **kwds)
return wrapper
@trace
def add(x, y):
"""Sum two numbers"""
return x + y
```
+++
The problem is that it does not really work
```python
>>> inspect.getfullargspec(add)
FullArgSpec(args=[], varargs='args', varkw='kwds',
defaults=None, kwonlyargs=[],
kwonlydefaults=None, annotations={})
```
and inspect.getfullargspec is telling the truth
```
>>> add.__code__.co_varnames
('args', 'kwds')
```
---
Enter the decorator module
```python
from decorator import decorator
@decorator
def trace(f, *args, **kwds):
print('Calling', f.__name__)
return f(*args, **kwds)
@trace
def add(a, b):
return a + b
>>> add.__code__.co_varnames
('a', 'b')
```
+++
Since 2017 you can also decorate coroutines
```python
@decorator
async def trace(coro, *args, **kwargs):
print('Calling %s', coro.__name__)
await coro(*args, **kwargs)
@trace
async def do_nothing(n):
for i in range(n):
await asyncio.sleep(1)
```
+++
Since 2018 you can define families of decorators with default arguments
```python
import warnings
from decorator import decorator
@decorator
def deprecated(func, message='', *args, **kw):
msg = '%s.%s has been deprecated. %s' % (
func.__module__, func.__name__, message)
if not hasattr(func, 'called'):
warnings.warn(msg, DeprecationWarning, stacklevel=2)
func.called = 0
func.called += 1
return func(*args, **kw)
```
+++
Usage with an without parenthesis
```
@deprecated('Use new_function instead')
def old_function():
'Do something'
@deprecated
def another_old_function():
'Do something else'
```
See more examples on http://decorator.readthedocs.io/en/latest/
|
