Python.get () and None

Question

I like python single liner:

u = payload.get("actor", {}).get("username", "")

The problem I am facing is that I can’t control what the “payload” is, other than knowing this vocabulary. So, if the "payload" does not have an "actor", or it does, and the actor has or does not have a "username", this single-line font is fine.

The problem, of course, arises when the payload has an actor, but the actor is not a dictionary.

Is there a way to do this comprehensively, as one liner, and consider the possibility that the "actor" may not be a dictionary?

Of course, I can check the type using "isinstance", but it's not so nice.

I don’t need one liner per se, just asking for the most effective way to ensure that “u” is populated without exception and without prior knowledge of what exactly is in the “payload”.

Answer 1

Using EAFP

At the suggestion of xnx, you can take advantage of the following python paradigm:

It’s easier to ask forgiveness than permission

You can use it on KeyError:

try:
    u = payload["actor"]["username"]
except (AttributeError, KeyError):
    u = ""

Using a proxy index wrapper

Sometimes it would be nice to have something like zero condition statements in Python. Using some helper class, this can be compressed into a single-line expression:

class Forgive:
  def __init__(self, value = None):
    self.value = value
  def __getitem__(self, name):
    if self.value is None:
      return Forgive()
    try:
      return Forgive(self.value.__getitem__(name))
    except (KeyError, AttributeError):
      return Forgive()
  def get(self, default = None):
    return default if self.value is None else self.value

data = {'actor':{'username': 'Joe'}}
print(Forgive(data)['actor']['username'].get('default1'))
print(Forgive(data)['actor']['address'].get('default2'))

ps: could be overridden __getattr__as well __getitem__, so you could even write Forgive(data)['actor'].username.get('default1').

Answer 2

:

try:
    u = payload.get("actor", {}).get("username", "")
except AttributeError:
    u = ""

Answer 3

hege_hegedus , , , if..else.

, payload, - , .

, payload, actor , .

u = ''
if 'actor' in payload and isinstance(payload['actor'], dict):
    u = payload['actor'].get('username', '')

- https://mail.python.org/pipermail/tutor/2011-January/081143.html

, ,

u = payload['actor'].get('username', '') if 'actor' in payload and isinstance(payload['actor'], dict) else ''

Answer 4

1 , . , .

: - payload.

1) actor, dict. isinstance try - - . u = get("username", "", payload.get("actor", {})) u = get("", payload, 'actor', 'username') ( payload).

2) - - , . dict UserDict ( Python3) , __getitem__.