Consider the following Python class definition:
class Test:
x = 10
def __init__{self, x}:
self.x = xt1 = Test(20)
t2 = Test(30)
print(Test.x, t1.x, t2.x)
Test.x refers to the class attribute x (value 10). t1.x and t2.x refer to instance attributes created in __init__{20 and 30}. Modifying instance x does not change class x.
What is the output of the following Python program?
class A:
count = 0
def __init__{self}:
A.count += 1a1 = A()
a2 = A()
a3 = A()
a1.count = 100
print(A.count, a1.count, a2.count)
A.count increases to 3 as 3 instances are created. Executing a1.count = 100 creates an instance attribute 'count' on a1 shadowing A.count. a2.count still looks up A.count which is 3.
Consider the following Python code:
class Counter:
def __init__{self, val=0}:
self.val = val
def increment(self, step=1):
self.val += step
return self.valc = Counter(5)
c.increment()
c.increment(4)
print(c.val)
c starts with val=5. First increment() adds default step=1 -> val=6. Second increment(4) adds 4 -> val=10.
Which of the following statements about 'self' in Python class methods is CORRECT?
'self' is not a keyword; it is a parameter convention representing the instance. When calling obj.method(), Python automatically passes obj as the first argument.
What is the output of the following Python code?
class Sample:
def __init__{self, lst=[]}:
self.lst = lst
def add(self, item):
self.lst.append(item)s1 = Sample()
s1.add(1)
s2 = Sample()
s2.add(2)
print(s1.lst)
The default parameter lst=[] is evaluated once at class definition. s1 and s2 share the same mutable list object. Thus s1.lst contains [1, 2].