'''Utility functions.'''

import inspect

from inject.exc import MultipleAttrsFound, NoAttrFound

def get_attrname_by_value(obj, attrvalue):

'''Return a name for object's attribute by its value.

It first iterates over instance's C{__dict__}, then fallbacks to

C{inspect.getmembers}. It is used by L{inject.injections.AttributeInjection}.

Example:

>>> class A(object):

>>> a = 'myvalue'

>>> get_attrname_by_value('myvalue')

'a'

>>>

@raise MultipleAttrsFound: If multiple attributes are found for a given value.

@raise NoAttrFound: If no attribute is found for a given value.

'''

def _get(items):

attrname = None

multiple = False

for name, value in items:

if value is not attrvalue:

continue

if attrname is not None:

if not isinstance(attrname, list):

attrname = [attrname]

multiple = True

attrname.append(name)

else:

attrname = name

if multiple:

raise MultipleAttrsFound('Multiple attributes %r found for '

'attrvalue %r in %r.' % (attrname, attrvalue, obj))

return attrname

attrname = _get(iter(obj.__dict__.items()))

if attrname is not None:

return attrname

# Fallback to a slow way.

attrname = _get(inspect.getmembers(obj))

if attrname is not None:

return attrname

raise NoAttrFound('Can\'t find an attribute in %r with the value %r.'

% (obj, attrvalue))