Python Count Elements in a List of Objects with Matching Attributes

python list object attributes count
FacesOfMu picture FacesOfMu · May 9, 2013 · Viewed 54k times · Source

I am trying to find a simple and fast way of counting the number of Objects in a list that match a criteria. e.g.

class Person:
    def __init__(self, Name, Age, Gender):
        self.Name = Name
        self.Age = Age
        self.Gender = Gender

# List of People
PeopleList = [Person("Joan", 15, "F"), 
              Person("Henry", 18, "M"), 
              Person("Marg", 21, "F")]

Now what's the simplest function for counting the number of objects in this list that match an argument based on their attributes? E.g., returning 2 for Person.Gender == "F" or Person.Age < 20.

Answer

jamylak picture jamylak · May 9, 2013 
class Person:
    def __init__(self, Name, Age, Gender):
        self.Name = Name
        self.Age = Age
        self.Gender = Gender


>>> PeopleList = [Person("Joan", 15, "F"), 
              Person("Henry", 18, "M"), 
              Person("Marg", 21, "F")]
>>> sum(p.Gender == "F" for p in PeopleList)
2
>>> sum(p.Age < 20 for p in PeopleList)
2

Related questions

Creating a list of objects in Python

I'm trying to create a Python script that opens several databases and compares their contents. In the process of creating that script, I've run into a problem in creating a list whose contents are objects that I've created. I've simplified …

Read More
Finding the index of an item in a list

Given a list ["foo", "bar", "baz"] and an item in the list "bar", how do I get its index (1) in Python?

Read More
How do I get the number of elements in a list?

Consider the following: items = [] items.append("apple") items.append("orange") items.append("banana") # FAKE METHOD: items.amount() # Should return 3 How do I get the number of elements in the list items?

Read More