Python：如何用getattr得到一个object属性属性？

Question

How do I evaluate

a = myobject.id.number

and return None if it myobject is None

with built-in getattr ? Maybe getattr(myobject, "id.number", None) ?

Answer 1

这应该可以很好地扩展到任何深度：

reduce(lambda obj, attr : getattr(obj, attr, None), ("id","num"), myobject)

Answer 2

getattr(getattr(myobject, "id", None), "number", None)

应该管用。

Answer 3

Here's a one-liner

a = myobject is not None and myobject.id.number or None

It doesn't check whether id is None, but that wasn't part of the original question.

Answer 4

A slightly over generic solution keeping in view all members:

if myobject and myobject.id and myobject.id.number:
    a = myobject.id.number
else:
    a = None

Answer 5

return myobject.id.number if myobject else None

Answer 6

my favorites are

from functools import reduce
try:
  a = reduce(getattr, ("id", "number"), myobject)
except AttributeError:
  a = None

or

from operator import attrgetter
try:
  a = attrgetter('id.number')(myobject)
except AttributeError:
  a = None

Answer 7

I use the following function which does it for any level.

def Resolve(object, attribute:str):
  """
  Resolve attribute of an object.
  """
  attribute_list = attribute.split(".")
  obj = object
  try:
    for att in attribute_list:
      obj = getattr(obj, att)
  except AttributeError:
    obj = None
    
  return obj

To use it you write:

a = Resolve(myobject, 'id.number')

The code simply splits the string using the the period character and loops through the attributes. If you had another level say `myobject.id.number.another' you would use:

a = Resolve(myobject, 'id.number.another')