check if an object is a list in Python

There are various way that we can use to tell whether an object is a list or not.

Using the isinstance() function

The builtin isinstnace() function is used to tell whether an object is an instance of the specified class. The function takes two arguments, the object and the target class. 

isinstance(obj, cls)

The function returns a boolean value(True or False) indicating whether obj is an instance of cls or not. We can use the function with the class list as the target parameter to tell whether the object is a list or not.

 object1 = 'Python'
object2 = (1, 2, 3)
object3 = [1, 2, 3, 4]

def is_list(obj):
    return isinstance(obj, list)

print(is_list(object1))
print(is_list(object2))
print(is_list(object3)) 

Using the type() Function

The builtin type() function is used to check the type/class of the object given as an argument. 

type(obj)

We can specify the object to be checked as the argument and then use a conditional statement to check whether the returned type is the builtin list class. 

 object1 = {'Python', 'Java', 'PHP'}
object2 = ('Python', 'Java','PHP')
object3 = ['Python', 'Java', 'PHP']

def is_list(obj):
    #use the type() function
    obj_type = type(obj)
    #use an if statement to check whether the returned value is the list class
    if obj_type == list:
        return  True

    return False

print(is_list(object1))
print(is_list(object2))
print(is_list(object3)) 

Using the __class__ attribute

Each object in Python contains an attribute __class__  that references the class/type the object  belongs to. In the case with lists  the __class__ attribute will reference the list class. We can use this attribute to tell if an object is a list or not depending on whether the __class__ attribute is set to list. 

 object1 = ['Python', 'Java', 'PHP']
object2 = (1, 2, 3)
object3 = {'one': 1, 'two': 2}

def is_list(obj):
   
    if obj.__class__ == list:
        return  True

    return False

print(is_list(object1))
print(is_list(object2))
print(is_list(object3))