Global name is not defined python recursion

In the line (l1 = sortList(head)) for recursion, I get NameError: global name 'sortList' is not defined. Could anyone point out where I did wrong?

class Solution:
    # @param head, a ListNode
    # @return a ListNode

    def sortList(self, head):
        if head == None or head.next == None:
            return head

        slow = head
        fast = head

        while fast != None and fast.next != None:
            slow = slow.next
            fast = fast.next.next
        fast = slow
        slow = slow.next
        fast.next = None
        l1 = sortList(head)
        l2 = sortList(slow)
        l = mergeTwoLists(l1, l2)
        return l

Korem

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asked Jun 18, 2014 at 17:46

5

sortList is a method of Solution, and doesn't exist independently. Use:

self.sortList(head)

and it would work.

answered Jun 18, 2014 at 17:49

KoremKorem

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You have not imported any function named sortList, so there only exists a sortList that can be called on a Solution object.

Use self.sortList. self is a variable used in python to refer to the current object. Much like this in other languages.

answered Jun 18, 2014 at 17:51

AlexAlex

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Change l1 = sortList(head) to l1 = self.sortList(head), and l2 = sortList(slow) to l2 = self.sortList(slow). sortList is defined in the Solution class and does not exist globally, that's why you need self to refer to the current Solution object.

answered Jun 18, 2014 at 17:49

timgebtimgeb

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I want to make a player that can shoot bullets. To do this i tried defining a shoot function that gets called when space bar is pressed. The function looks like this (p is the player object btw):

class bullet:
    def __init__(self):
        self.x = None
        self.y = None
        self.radius = 10
        self.shooting = False
        self.speed = 5

    def shoot(self):
        self.shooting = True
        if  self.shooting == True:
            self.x = (p.x + 60)
            self.y = (p.y + 25)
            self.x += self.speed
            self.y += self.speed
            pygame.draw.circle(d, (0, 0, 0), (self.x, self.y), self.radius)

        shoot()

I was hoping that the function would keep calling itself and the bullet would keep moving forward. However what actually happens is when i press space, it gives me an error

    shoot()
NameError: name 'shoot' is not defined

How i called the function:

while True:
    d.fill((98, 98, 98))
    p.draw()

    for event in pygame.event.get():
        pass

    if event.type == pygame.KEYDOWN:
        if event.key == pygame.K_SPACE:
            b.shoot()

Something i observed is that if i remove the recursion shoot() at the end of the shoot() function, it runs but the bullet stays in the same place as long as the space is being held down(as expected as recursion was removed). How can i fix this problem? Thanks

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Answer

shoot is not a function, strictly speaking. It’s an instance method, and must be invoked from a bullet object. You need to use

for recursion.

However, this is a poor way to keep the bullet moving. This is a job for a loop. Recursion is best used when you’re calling the routine with a smaller version of the problem; this is just a continuance.

    while self.shooting == True:
        self.x = (p.x + 60)
        self.y = (p.y + 25)
        self.x += self.speed
        self.y += self.speed
        pygame.draw.circle(d, (0, 0, 0), (self.x, self.y), self.radius)

This raises the question of how you intend to quit moving the bullet. You need something like

        self.shooting = (self.x <= x_limit) and 
                        (self.y <= y_limit)

Where x/y_limit are the upper bounds in that movement direction.