How to check if instance object's attribute within a list is equal to a value

Question

I have an arbitrary number of objects created from this class:

class Person:
    def __init__(self, name, email):
        self.name = name
        self.email = email

I have a list of these objects:

myList = []
JohnDoe = Person("John Doe", "[email protected]")
BobbyMcfry = Person("Bobby Mcfry", "[email protected]")
WardWilkens = Person("Ward Wilkens", "[email protected]")
myList.append(JohnDoe)
myList.append(BobbyMcfry)
myList.append(WardWilkens)

I am wanting to check if someone exists, and if so, return their attributes - if not, say so:

x = input("Who to check for? ")
for i in myList:
    if i.name == x:
        print("Name: {0}\nEmail: {1}".format(i.name, i.email))
    else:
        print("{0} is not on the manifest.".format(x))

This kind of works, but returns one or the other for each Person in myList - I only want one return...

I realize I need to do some sort of

if val in myList:....

But I'm having trouble how to word what "val" should be without iterating through each object

You could add a break and make your loop greedy and stop on the first match. — sean
– sean, Commented Dec 20, 2012 at 23:07

Andrew Clark · Accepted Answer · 2012-12-20 23:27:06Z

5

Using the loop is fine, you just need to handle the case where none of the names matched, you can do this easily using break and else:

x = input("Who to check for? ")
for i in myList:
    if i.name == x:
        print("Name: {0}\nEmail: {1}".format(i.name, i.email))
        break
else:
    # this is only run if 'break' was not executed inside of the loop
    print("{0} is not on the manifest.".format(x))

Depending on what you use the list for, you might be better of using a dictionary to link names to Person objects:

myDict = {}
JohnDoe = Person("John Doe", "[email protected]")
BobbyMcfry = Person("Bobby Mcfry", "[email protected]")
WardWilkens = Person("Ward Wilkens", "[email protected]")
for person in [JohnDoe, BobbyMcfry, WardWilkens]:
    myDict[person.name] = person

x = input("Who to check for? ")
person = myDict.get(x)
if person:
    print("Name: {0}\nEmail: {1}".format(person.name, person.email))
else:
    print("{0} is not on the manifest.".format(x))

edited Dec 20, 2012 at 23:27

answered Dec 20, 2012 at 23:09

Andrew Clark

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3 Comments

randomusername Over a year ago

Worked perfectly. I didn't realize the else would work with anything other than a linked "if" - nice to know.

Silas Ray Over a year ago

If you are going to make a dict accessor to the person list, rather than duplicating the names, either make a function that creates and inserts in to the dict using a parameterized name that you only hardcode once, or wrap the collection in an object that overrides __getitem__ to retrieve a person with a name matching the provided key.

randomusername Over a year ago

Appreciate the dictionary example also - I was earlier trying to link names to the objects but did not know how.

Silas Ray · Accepted Answer · 2012-12-20 23:12:22Z

1

Could use itertools.

try:
    found_person = itertools.dropwhile(lambda person: person.name != search_name, people).next()
except StopIteration:
    found_person = None

answered Dec 20, 2012 at 23:12

Silas Ray

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