How to extract sentences from one text with only 1 named entity using spaCy?

Question

I have a list of sentences and I want to be able to append only the sentences with 1 "PERSON" named entity using spaCy. The code I used was as follows:

test_list = []
for item in sentences: #for each sentence in 'sentences' list
  for ent in item.ents: #for each entity in the sentence's entities 
    if len(ent in item.ents) == 1: #if there is only one entity
      if ent.label_ == "PERSON": #and if the entity is a "PERSON"
        test_list.append(item) #put the sentence into 'test_list'

But then I get:

TypeError: object of type 'bool' has no len()

Am I doing this wrong? How exactly would I complete this task?