util.py

WebCore common utilities.

 


            		
          

          

            
              

                
              

              
Imports

            		
            
              
from __future__ import unicode_literals

from threading import RLock

from marrow.package.canonical import name



            		
          

          

            
              

                
              

              
Module Global Constants

            		
            
              
sentinel = object()  # A singleton value to allow `None` as a legal value.



            		
          

          

            
              

                
              

              
Utility Functions

            		
            
              


            		
          

          

            
              

                
              

              
Attempt to resolve the canonical name for an object, falling back on the repr() if unable to do so.

            		
            
              
def safe_name(thing):
	try:
		return name(thing)
	except:
		return repr(thing)



            		
          

          

            
              

                
              

              
Context-Related Utility Classes

            		
            
              


            		
          

          

            
              

                
              

              
Lazily record the result of evaluating a function and cache the result.


This is a non-data descriptor which tells Python to allow the instance dict to override. Intended to be used
by extensions to add zero-overhead (if un-accessed) values to the context.

            		
            
              
class lazy(object):
	



            		
          

          

            
              

                
              

              
            		
            
              
	def __init__(self, func, name=None, doc=None):
		self.__name__ = name or func.__name__
		self.__module__ = func.__module__
		self.__doc__ = func.__doc__
		self.lock = RLock()
		self.func = func
	



            		
          

          

            
              

                
              

              
            		
            
              
	def __get__(self, instance, type=None):
		if instance is None:  # Allow direct access to the non-data descriptor via the class.
			return self
		
		with self.lock:  # Try to avoid situations with parallel thread access hammering the function.
			value = instance.__dict__.get(self.__name__, sentinel)
			
			if value is sentinel:
				value = instance.__dict__[self.__name__] = self.func(instance)
		
		return value