I want to append an item to the list in Class A but when I call the list after the process, it just return an empty list. How exactly can I successfully append an item?

This is what I tried. I implement lst.append inside the getAnswer method but the appending was unsuccessful. Note that I only included snippet of my code because there are other things going on there. I am just concerned on knowing how can I successfully to the appending function.

class A:
  lst = []

class B:
  *#I implemented distance formula here*

class C: 
  def __init__(self, pt, tolerance):
    self.pt = pt

  def getAnswer(self, tolerance):
    self.tolerance = tolerance

    d = B(p1,p2).dist
    if d <= self.tolerance:
       lst.append(p2)

p_list = [p1, p2]
a = C(p_list, 7)

A.lst

CodePudding user response：

Theres lots of things wrong with your question so I've bullet pointed them and then updated your snippet.

• your instance of C is called a which is confusing
• You pass in tolerance to your C initializer and never use it,
• lst is a class variable of A but you aren't using it, instead you're making a new variable of the same name in your getAnswer function
• getAnswer is never called.
• getAnswer never "gets" anything so the function name is a bit misleading (havent modified)
• you initiate B with two variables p1,p2 which don't exist in the scope of the function, but already exist in your pt list

class A:
  lst = []

class B:
  *#I implemented distance formula here*

class C: 
  def __init__(self, pt):
    self.pt = pt
    self.tolerance = None

  def getAnswer(self, tolerance):
    self.tolerance = tolerance

    d = B(self.pt[0],self.pt[1]).dist
    if d <= self.tolerance:
       A.lst.append(p2)

p_list = [p1, p2]
c = C(p_list)
c.getAnswer(7)
A.lst

Whilst the above will update your list, its still odd to have C change A's list, I've left it as is because there are valid use cases and the variable names are too vague too suggest otherwise.

CodePudding user response：

It does not work, because lst is a local variable inside the class/function. I would do:

class A:
    global lst
    lst = []
class C:
    #init
    def getAnswer(self, tolerance):
        #stuff
        #if
            lst.append(p2)

Here is a test:

>>> class A:
    global lst
    lst = []

>>> class C:
    def __init__(self):
        lst.append("This is appended to the list!")

>>> C()
<__main__.C object at 0x0000021D25CF5640>
>>> """I just called the C __init__ function, let's see if it worked"""
"I just called the C __init__ function, let's see if it worked"
>>> print(lst)
['This is appended to the list!']
>>> """Yay!"""
'Yay!'
>>>