Book Excerpt: The Python Standard Library by Example

Acquiring Function Properties for Decorators

Updating the properties of a wrapped callable is especially useful when used in a decorator, since the transformed function ends up with properties of the original “bare” function.

import functools 

def	show_details(name, f): 
      """Show details of a callable object.""" 
      print %s:’ % name 
      print ’ object:’,f 
      print ’ __name__:’, 
      try: 
           print f.__name__ 
      except AttributeError: 
           print ’(no __name__)’ 
      print ’ __doc__’, repr(f.__doc__) 
      print 
      return 

def	simple_decorator(f): 
      @functools.wraps(f)
      def decorated(a=’decorated defaults’, b=1): 
          print ’ decorated:’, (a, b) 
          print ’’,
          f(a, b=b) 
          return 
      return decorated 

def	myfunc(a, b=2): 
     "myfunc() is not complicated" 
      print ’ myfunc:’, (a,b) 
      return 

# The raw function 
show_details(’myfunc’, myfunc) 
myfunc(’unwrapped, default b’) 
myfunc(’unwrapped, passing b’, 3) 
print 

# Wrap explicitly 
wrapped_myfunc = simple_decorator(myfunc) 
show_details(’wrapped_myfunc’, wrapped_myfunc) 
wrapped_myfunc() 
wrapped_myfunc(’args to wrapped’, 4) 
print 

# Wrap with decorator syntax 
@simple_decorator 
def decorated_myfunc(a, b): 
    myfunc(a, b) 
    return 

show_details(’decorated_myfunc’, decorated_myfunc) 
decorated_myfunc() 
decorated_myfunc(’args to decorated’, 4) 

functools provides a decorator, wraps(), that applies update_wrapper() to the decorated function.

$ python functools_wraps.py 


myfunc:
 object: <function myfunc at 0x100da3488>
 __name__: myfunc
 __doc__ ’myfunc() is not complicated’ 

 myfunc: (’unwrapped, default b’, 2)
 myfunc: (’unwrapped, passing b’, 3) 

wrapped_myfunc:
 object: <function myfunc at 0x100da3500>
 __name__: myfunc
 __doc__ ’myfunc() is not complicated’ 

decorated: (’decorated defaults’, 1)
   myfunc: (’decorated defaults’, 1) 
decorated: (’args to wrapped’, 4)
   myfunc: (’args to wrapped’, 4) 

decorated_myfunc:
 object: <function decorated_myfunc at 0x100da35f0>
 __name__: decorated_myfunc
 __doc__ None 

 decorated: (’decorated defaults’, 1)
    myfunc: (’decorated defaults’, 1)
 decorated: (’args to decorated’, 4)
    myfunc: (’args to decorated’, 4) 
______________________

Webinar
One Click, Universal Protection: Implementing Centralized Security Policies on Linux Systems

As Linux continues to play an ever increasing role in corporate data centers and institutions, ensuring the integrity and protection of these systems must be a priority. With 60% of the world's websites and an increasing share of organization's mission-critical workloads running on Linux, failing to stop malware and other advanced threats on Linux can increasingly impact an organization's reputation and bottom line.

Learn More

Sponsored by Bit9

Webinar
Linux Backup and Recovery Webinar

Most companies incorporate backup procedures for critical data, which can be restored quickly if a loss occurs. However, fewer companies are prepared for catastrophic system failures, in which they lose all data, the entire operating system, applications, settings, patches and more, reducing their system(s) to “bare metal.” After all, before data can be restored to a system, there must be a system to restore it to.

In this one hour webinar, learn how to enhance your existing backup strategies for better disaster recovery preparedness using Storix System Backup Administrator (SBAdmin), a highly flexible bare-metal recovery solution for UNIX and Linux systems.

Learn More

Sponsored by Storix