choose a defined attribute in a nested object in jinja

Question

I'm looking for a convenient, elegant way to display an attribute of nested object, choosing the first one which is defined.

Something like this :

from jinja2 import Template

o1 = { "a" : { "b" : { "c" : "John Doe" } } }
o2 = { "e" : { "f" : "John Doe" } }
o3 = { }

template = Template("""Hello {{ o.a.b.c or o.e.f or "John Doe" }}!""")

for o in [o1, o2, o3]:
    r = template.render(o=o)
    print(r)

Each print should output "Hello John Doe!", the first does. But then it fails with a jinja2.exceptions.UndefinedError: 'dict object' has no attribute 'a'.

I have tried to use defined but it would imply multiple if statement. Which I'd like to avoid.

Answer 1

this seems to work fine

>>> template = Template("""Hello {{ o.get('a',{}).get('b',{}).get('c',None) or o.get('e',{}).get('f',None) or "John Doe" }}!""")
>>> template.render(o=o2)
u'Hello John Doe!'
>>> template.render(o=o1)
u'Hello John Doe!'
>>> template.render(o=o3)
u'Hello John Doe!'

otherwise as soon as a key does not exist it raises an error that short circuits the rest of the logic ... much like trying to index into a dictionary with a non-existant key