How to create a list of objects?

Question

How do I go about creating a list of objects (class instances) in Python?

Or is this a result of bad design? I need this cause I have different objects and I need to handle them at a later stage, so I would just keep on adding them to a list and call them later.

• Skurmedel: Do you mean a list of type objects ([type(x), ... ]) or instances of a class ([1, 2, 3])?
• user225312: @Skurmedel: class instances. I mentioned it specifically in the question :)
• Skurmedel: @Alfred: hehe, I just find class instances a bit ambiguous, but I see what you mean now through the selected answer :P

Answer 1

Storing a list of object instances is very simple

class MyClass(object):
 def __init__(self, number):
 self.number = number
my_objects = []
for i in range(100):
 my_objects.append(MyClass(i))
# Print the number attribute of each instance
for obj in my_objects:
 print(obj.number)

• Brad English: Where you pass "object" in the first line, is that an actual object or just a number signifying that object instance's number? If I were to write my_objects(1), I would call to the first object, but I don't think the 1 being passed in is an object. This might be entirely orthogonal to the educational purposes of the original response, but it would help me on a different, related topic I'm struggling with. Thanks.
• SIGSTACKFAULT: T'was hoping there was a shiny special syntax for this :(
• ChootsMagoots: @Brad English, that indicates that MyClass inherits the properties of an object
• ChootsMagoots: The i in MyClass (i) refers to the number in the class's __init__ function.

Answer 2

You can create a list of objects in one line using a list comprehension.

class MyClass(object): pass
objs = [MyClass() for i in range(10)]
print(objs)

• Galaxy: This is really clean syntax.
• Brainless: Slight detail: objs = [MyClass(i) for i in range(10)]
• cryptoplex: @Brainless, in this answer, the MyClass() initializer does not take an argument (in one of the other answers, it does...).
• Martin CR: The usual python idiom is to use _ for loop variables that aren't referenced in the loop body (i.e. objs = [MyClass() for _ in range(10)])

Answer 3

The Python Tutorial discusses how to use lists.

Storing a list of classes is no different than storing any other objects.

def MyClass(object):
 pass
my_types = [str, int, float, MyClass]

Answer 4

In Python, the name of the class refers to the class instance. Consider:

class A: pass
class B: pass
class C: pass
lst = [A, B, C]
# instantiate second class
b_instance = lst[1]()
print b_instance

Answer 5

I have some hacky answers that are likely to be terrible... but I have very little experience at this point.

a way:

class myClass():
 myInstances = []
 def __init__(self, myStr01, myStr02):
 self.myStr01 = myStr01
 self.myStr02 = myStr02
 self.__class__.myInstances.append(self)
myObj01 = myClass("Foo", "Bar")
myObj02 = myClass("FooBar", "Baz")
for thisObj in myClass.myInstances:
 print(thisObj.myStr01)
 print(thisObj.myStr02)

A hack way to get this done:

import sys
class myClass():
 def __init__(self, myStr01, myStr02):
 self.myStr01 = myStr01
 self.myStr02 = myStr02
myObj01 = myClass("Foo", "Bar")
myObj02 = myClass("FooBar", "Baz")
myInstances = []
myLocals = str(locals()).split("'")
thisStep = 0
for thisLocalsLine in myLocals:
 thisStep += 1
 if "myClass object at" in thisLocalsLine:
 print(thisLocalsLine)
 print(myLocals[(thisStep - 2)])
 #myInstances.append(myLocals[(thisStep - 2)])
 print(myInstances)
 myInstances.append(getattr(sys.modules[__name__], myLocals[(thisStep - 2)]))
for thisObj in myInstances:
 print(thisObj.myStr01)
 print(thisObj.myStr02)

Another more 'clever' hack:

import sys
class myClass():
 def __init__(self, myStr01, myStr02):
 self.myStr01 = myStr01
 self.myStr02 = myStr02
myInstances = []
myClasses = {
 "myObj01": ["Foo", "Bar"],
 "myObj02": ["FooBar", "Baz"]
 }
for thisClass in myClasses.keys():
 exec("%s = myClass('%s', '%s')" % (thisClass, myClasses[thisClass][0], myClasses[thisClass][1]))
 myInstances.append(getattr(sys.modules[__name__], thisClass))
for thisObj in myInstances:
 print(thisObj.myStr01)
 print(thisObj.myStr02)

Answer 6

if my_list is the list that you want to store your objects in it and my_object is your object wanted to be stored, use this structure:

my_list.append(my_object)

Answer 7

We have class for students and we want make list of students that each item of list is kind of student

class student :
 def __init__(self,name,major):
 self.name=name
 self.major=major
students = []
count=int(input("enter number of students :"))
#Quantify
for i in range (0,count):
 n=input("please enter name :")
 m=input("please enter major :")
 students.append(student(n,m))
#access
for i in students:
 print (i.name,i.major)

• Community: As it’s currently written, your answer is unclear. Please edit to add additional details that will help others understand how this addresses the question asked. You can find more information on how to write good answers in the help center.

Answer 8

I think what you're of doing here is using a structure containing your class instances. I don't know the syntax for naming structures in python, but in perl I could create a structure obj.id[x] where x is an incremented integer. Then, I could just refer back to the specific class instance I needed by referencing the struct numerically. Is this anything in the direction of what you're trying to do?