Python：类函数中的全局变量

Question

class LinkedList():
    
    def __init__(self):
        self.head = None
    
    def loopCheck(self):
        global fast
        slow = self.head
        fast = self.head 
        while(fast.next!=None):
            slow = slow.next
            fast = fast.next.next
            if slow.data == fast.data:
                return True
            
        return False
    def lenLoop(self):
        if not(self.loopCheck):
            print("No loop found")
        else:
            print(fast.data)

The variable fast is not getting recognised in the lenLoop() function. How do I make a variable global inside a class?

Answer 1

You can declare it in the constructor of your class as self.fast as you have done with self.head . Intuitively speaking, self is like a dictionary which stores the values of the variables along with their names so that they can be accessed anywhere within the class.

Answer 2

Because you are not calling your function. Try self.loopCheck() instead of self.loopCheck .

def lenLoop(self):
    if not(self.loopCheck()):
        print("No loop found")
    else:
        print(fast.data)

Output

1 -> 2 -> 3 -> None
No loop found