理解 pdb 输出 - 问题可能是由于 repr_

Question

我不明白使用 Python 调试器时记录的内容。进入调试器后，我到达了 ###Line where I get the output### [如代码所示] 之后的行。为什么我的输出不是我预期的？我认为这可能是由于 repr 并且链接列表是元素的容器。

我的输出

Value :2
Next: Value :3
Next: None
-----

-----

我预期的输出

Value :2
Next: 3

我的代码

element.py

class Element:
    def __init__(self, value):
        self.value = value
        self.next = None

    def __repr__(self):
        string = "Value :" + str(self.value) + "\n" + "Next: " + str(self.next) + "\n" + "-----" + '\n'
        return string

链表class和pdb

linked_list.py

from pdb import set_trace
from element import Element

class LinkedList:
    def __init__(self, head=None):
        self.head = head

def append(self, new_element):
    current = self.head

    if self.head:
        while current.next:
            current = current.next
        current.next = new_element
    else:
        self.head = new_element

def get_position(self, position):
    """Get an element from a particular position.
    Assume the first position is "1".
    Return "None" if position is not in the list."""

    # Handle bad input
    if position <= 0 or type(position) is not int:
        raise ValueError('Enter an integer that is greater than 0')

    # Linked list is empty
    if not self.head:
        return None

    counter = 0
    current = self.head

    while counter <= position and current:
        counter += 1
        if counter == position:
            return current
        current = current.next

    return None

def insert(self, new_element, position):
    """Insert a new node at the given position.
    Assume the first position is "1".
    Inserting at position 3 means between
    the 2nd and 3rd elements."""
    set_trace()
    if position == 1:
        new_element.next = self.head.next
        # print('pp', self.head.next.value)
        ###Line where I get the output###
        self.head = new_element
        return

    element = self.get_position(position - 1)

    new_element.next = element.next

    element.next = new_element


def delete(self, value):
    """Delete the first node with a given value."""
    # set_trace()
    current = self.head

    # first element has the value
    if current.value == value:
        self.head = current.next
        return

    prior = self.head

    while current:
        if current.value == value:
            prior.next = current.next

        prior =  current
        current = current.next

def __repr__(self):
    # set_trace()
    current = self.head
    string = ""
    counter = 1
    while current:
        string += str(counter) + ': ' + str(current.value) + '\n' + '-'* 10 + '\n'
        current = current.next
        counter += 1

    return string

  # def __repr__(self):
  #   pass

if __name__ == "__main__":

# Test cases
# Set up some Elements
e1 = Element(1)
e2 = Element(2)
e3 = Element(3)
e4 = Element(4)

# Start setting up a LinkedList
ll = LinkedList(e1)
ll.append(e2)
ll.append(e3)

print(ll)
# Test get_position
# Should print 3
print(ll.head.next.next.value)
# Should also print 3
print(ll.get_position(3).value)

# set_trace()
# Test insert
# set_trace()
ll.insert(e4,1)
print(ll)
# ll.insert(e4,3)
# # Should print 4 now
print(ll.get_position(3).value)

# # # Test delete

# ll.delete(1)
# # # Should print 2 now
# # # set_trace()
# print(ll.get_position(1).value)
# # Should print 4 now
# print(ll.get_position(2).value)
# # Should print 3 now
# print(ll.get_position(3).value)
# 3
# 3
# 4 # insert
# 2 # after delete

Answer 1

3 是 self.next.value。你没有写str(self.next.value)；你写了 str(self.next).

self.next 是一个 Element，所以在 Next: 之后，您会看到下一个元素的 repr。

# Part marked in parentheses is the repr of the next element.
Value :2
Next: (Value :3
Next: None)

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