adding an element to a linked list python

Question

I am trying to run this test on my add function for my linked list:

>>> test = FrequencyList()
>>> test.add('a', 3)
>>> test
Frequency List -> Frequency('a', 3) -> None
>>> test.add('b', 2)
>>> test
Frequency List -> Frequency('a', 3) -> Frequency('b', 2) -> None

But my output is just Frequency List -> None with the error: File "x-wingide-python-shell://130365360/2", line 75, in add - TypeError: init() takes 1 positional argument but 3 were given

Answer 1

You need to change FrequencyList by Frequency, but you also have to add it correctly. This example could work:

class FrequencyList(object):
 """Stores a collection of Frequency objects as a linked list."""
 def __init__(self):
 """ Creates an empty FrequencyList """
 self.head = None
 self.last = None
 def add(self, letter, frequency=1):
 temp = Frequency(letter, frequency)
 if self.head is None:
 self.head = temp
 self.last = temp
 else:
 self.last.next_node = temp
 self.last = temp
 def __repr__(self):
 if self.head is not None:
 next_freq = self.head
 data = "Frequency List -> "
 while next_freq is not None:
 data += repr(next_freq) + " -> "
 next_freq = next_freq.next_node
 data += "None"
 return data
 else:
 return "Empty List"
class Frequency(object):
 """
 Stores a letter:frequency pair.
 """
 def __init__(self, letter, frequency):
 self.letter = letter
 self.frequency = frequency
 # The next Frequency object when stored as part of a linked list
 self.next_node = None
 def __repr__(self):
 return 'Frequency({}, {})'.format(repr(self.letter), repr(self.frequency))
test = FrequencyList()
test.add('a', 3)
print(test)
test.add('b', 2)
print(test)

Answer 2

If add means is adding node to a list, the solution is to replace temp = FrequencyList(letter, frequency) with temp = Frequency(letter, frequency).