Python member variable as parameter

Question

I have a class A with a member function a and a parameter p with a default value. I want this default value to be the member variable of the class.

class A:
   def a(self, p = self.b):
       print p

However it crashed with the information:

<ipython-input-2-a0639d7525d3> in A()
      1 class A:
----> 2     def a(self, p = self.b):
      3         print p
      4

NameError: name 'self' is not defined

I want to know whether I can pass a member variable as a default parameter to the member function?

alecxe · Accepted Answer · 2016-10-08 03:25:50Z

3

One option would be to set the default p value as None and check its value in the method itself:

class A:
    def __init__(self, b):
        self.b = b

    def a(self, p=None):
        if p is None:
            p = self.b
        print(p)

Demo:

In [1]: class A:
    ...:     def __init__(self, b):
    ...:         self.b = b
    ...: 
    ...:     def a(self, p=None):
    ...:         if p is None:
    ...:             p = self.b
    ...:         print(p)
    ...:         

In [2]: a = A(10)

In [3]: a.a()
10

In [4]: a.a(12)
12

answered Oct 8, 2016 at 3:25

alecxe

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3 Comments

maple Over a year ago

I have several parameters and I don't want to judge them one by one. Can this be wraped into a function? one problem is that if they are warped into a function, the value variable can not be set in a function.

alecxe Over a year ago

@maple okay, yeah, that does not scale that good. Do you want all the method arguments have the same self.b default value? Thanks.

maple Over a year ago

I want they have different default value and can be set in the funciton.

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