chained attrgetter

[David S.]

Does something like operator.getattr exist to perform a chained attr
lookup?

I came up with the following, but I can not help but think it is
already done and done better.

Peace,
David S.

def compose(funcs):
""" return composite of funcs
this does not support extended call syntax, so each func can
only take a single arg

>>> from operator import add
>>> funcs = [lambda x:add('ANSWER: ', str(x)), lambda x:add(x,100)]
>>> compose(funcs)(9)

'ANSWER: 109'

"""
def _func(arg):
return reduce(lambda v,f: f(v), iter(funcs[::-1]), arg)
return _func

def chained_attrgetter(cattr):
""" 'Hey, now!'

"""
return compose([attrgetter(attr) for attr in
cattr.split('.')[::-1]])

 

[Alexey Borzenkov]

Does something like operator.getattr exist to perform a chained attr
lookup?

Do you mean something like

class cattrgetter:
def __init__(self, name):
self.names = name.split('.')
def __call__(self, obj):
for name in self.names:
obj = getattr(obj, name)
return obj

?

 

[Brian Beck]

Do you mean something like

class cattrgetter:
def __init__(self, name):
self.names = name.split('.')
def __call__(self, obj):
for name in self.names:
obj = getattr(obj, name)
return obj

I'll raise you one:

def cattrgetter(attr):
return lambda obj: reduce(getattr, attr.split('.'), obj)

py> class A: pass
py> a = A
py> a.b = A
py> a.b.c = "Hey!"
py> cattrgetter('b.c')(a)
'Hey!'

 

[Brian Beck]

Does something like operator.getattr exist to perform a chained attr
lookup?

I came up with the following, but I can not help but think it is
already done and done better.

You were on the right track, but the built-in getattr is a perfectly
good argument to reduce(), using operator.attrgetter just makes the
definition more complicated (see my other post).

 

[David S.]

Ah, pretty Python.

Thanks, all.