How to define default list in python class

Question

class points():

  def __init__(self,a1,b1,c1,d1):
    self.a1=a1
    self.b1=b1
    self.c1=c1
    self.d1=d1


  def plot(self):
    xs=[self.a1[0],self.b1[0],self.c1[0],self.d1[0]]                           
    ys=[self.a1[1],self.b1[1],self.c1[1],self.d1[1]] 
    print(xs)
    print(ys)                           
    colors=['c','m','b','y']

a1=points([1,2],[2],[3,4],[4,5])
a1.plot()

How to define a default list so that when I am not providing value to b1[1] , it doesn't give error?

You can't. list doesn't have a counterpart to dict.get. Either validate that a correct list is assigned to self.b1 in the first place, or handle the possible IndexError in points.plot. — chepner
– chepner, Commented Sep 15, 2022 at 19:54

Lucas M. Uriarte · Accepted Answer · 2022-09-15 20:03:15Z

1

this could be an option but I am not sure about the question.

class points():

  def __init__(self,a1,b1,c1,d1):
    self.a1=a1
    self.b1=b1
    self.c1=c1
    self.d1=d1


  def plot(self, default_val=0):
    elements = [self.a1,self.b1,self.c1,self.d1]
    xs=[val[0] if type(val) is list and len(val)>0 else default_val for val in elements]                           
    ys=[val[1] if type(val) is list and len(val)>1 else default_val for val in elements] 
    print(xs)
    print(ys)                           
    colors=['c','m','b','y']

a1=points([1,2],[2],[3,4],[4,5])

a1.plot()
>>>
[1, 2, 3, 4]
[2, 0, 4, 5]

a1.plot(14)
>>>
[1, 2, 3, 4]
[2, 14, 4, 5]

answered Sep 15, 2022 at 20:03

Lucas M. Uriarte

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Comments

Deepak Tripathi · Accepted Answer · 2022-09-15 20:12:29Z

You can try this hack as well

from collections import defaultdict
default_value = 0

class points():

  def __init__(self,a1,b1,c1,d1, default_value=default_value):
    self.b1=defaultdict(lambda : default_value, enumerate(b1))
    self.a1=defaultdict(lambda : default_value,enumerate(a1))
    self.c1=defaultdict(lambda : default_value,enumerate(c1))
    self.d1=defaultdict(lambda : default_value,enumerate(d1))


  def plot(self):
    xs=[self.a1[0],self.b1[0],self.c1[0],self.d1[0]]                           
    ys=[self.a1[1],self.b1[1],self.c1[1],self.d1[1]] 
    print(xs)
    print(ys)                           
    colors=['c','m','b','y']

a1=points([1,2],[2],[3,4],[4,5], default_value=default_value)
a1.plot()

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