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How to avoid explicit 'self' in Python?

I have been learning Python by following some pygame tutorials.

Therein I found extensive use of the keyword self, and coming from a primarily Java background, I find that I keep forgetting to type self. For example, instead of self.rect.centerx I would type rect.centerx, because, to me, rect is already a member variable of the class.

The Java parallel I can think of for this situation is having to prefix all references to member variables with this.

Am I stuck prefixing all member variables with self, or is there a way to declare them that would allow me to avoid having to do so?

Even if what I am suggesting isn't pythonic, I'd still like to know if it is possible.

I have taken a look at these related SO questions, but they don't quite answer what I am after:

Answer*

Previous answers are all basically variants of "you can't" or "you shouldn't". While I agree with the latter sentiment, the question is technically still unanswered. 

Furthermore, there are legitimate reasons why someone might want to do something along the lines of what the actual question is asking. One thing I run into sometimes is lengthy math equations where using long names makes the equation unrecognizable. Here are a couple ways of how you could do this in a canned example:

 import numpy as np
 class MyFunkyGaussian() :
 def __init__(self, A, x0, w, s, y0) :
 self.A = float(A)
 self.x0 = x0
 self.w = w
 self.y0 = y0
 self.s = s
 
 # The correct way, but subjectively less readable to some (like me) 
 def calc1(self, x) :
 return (self.A/(self.w*np.sqrt(np.pi))/(1+self.s*self.w**2/2)
 * np.exp( -(x-self.x0)**2/self.w**2)
 * (1+self.s*(x-self.x0)**2) + self.y0 )
 
 # The correct way if you really don't want to use 'self' in the calculations
 def calc2(self, x) :
 # Explicity copy variables
 A, x0, w, y0, s = self.A, self.x0, self.w, self.y0, self.s
 sqrt, exp, pi = np.sqrt, np.exp, np.pi
 return ( A/( w*sqrt(pi) )/(1+s*w**2/2)
 * exp( -(x-x0)**2/w**2 )
 * (1+s*(x-x0)**2) + y0 )
 
 # Probably a bad idea...
 def calc3(self, x) :
 # Automatically copy every class vairable
 for k in self.__dict__ : exec(k+'= self.'+k)
 sqrt, exp, pi = np.sqrt, np.exp, np.pi
 return ( A/( w*sqrt(pi) )/(1+s*w**2/2)
 * exp( -(x-x0)**2/w**2 )
 * (1+s*(x-x0)**2) + y0 )
 
 g = MyFunkyGaussian(2.0, 1.5, 3.0, 5.0, 0.0)
 print(g.calc1(0.5))
 print(g.calc2(0.5))
 print(g.calc3(0.5))


The third example - i.e. using `for k in self.__dict__ : exec(k+'= self.'+k)` is basically what the question is actually asking for, but let me be clear that I don't think it is generally a good idea.

For more info, and ways to iterate through class variables, or even functions, see answers and discussion to [this question][1]. For a discussion of other ways to dynamically name variables, and why this is usually not a good idea see [this blog post][2].

**UPDATE:** There appears to be [no way][3] to dynamically update or change locals in a function in Python3, so calc3 and similar variants are no longer possible. The only python3 compatible solution I can think of now is to use `globals`:
 
 def calc4(self, x) :
 # Automatically copy every class variable in globals
 globals().update(self.__dict__)
 sqrt, exp, pi = np.sqrt, np.exp, np.pi
 return ( A/( w*sqrt(pi) )/(1+s*w**2/2)
 * exp( -(x-x0)**2/w**2 )
 * (1+s*(x-x0)**2) + y0 )

Which, again, would be a terrible practice in general.



 [1]: https://stackoverflow.com/questions/11637293/iterate-over-object-attributes-in-python
 [2]: http://stupidpythonideas.blogspot.com/2013/05/why-you-dont-want-to-dynamically-create.html
 [3]: https://stackoverflow.com/questions/1450275/any-way-to-modify-locals-dictionary

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13

Brilliant! This is the most (only?) correct answer. +1 You also uniquely give a practical reason for doing it. +1i

David Lotts
– David Lotts

2018年08月16日 15:20:45 +00:00
Commented Aug 16, 2018 at 15:20
2

After creating a class and moving the code inside of it : now all of the methods and variables are no longer recognized (no self. ..) I am reminded of yet another reason python and I do not get along. Thanks for this as an idea. It does not fix the problem /headache / unreadability overall but provides a modest workaround.

WestCoastProjects
– WestCoastProjects

2019年05月21日 13:57:40 +00:00
Commented May 21, 2019 at 13:57
Why not just update locals instead of using exec?

Nathan
– Nathan

2020年03月13日 17:14:41 +00:00
Commented Mar 13, 2020 at 17:14
1

I tried locals().update(self.__dict__) in python 2 and 3, but it didn't work. In python3 even the 'exec' trick isn't an option anymore. On the other hand, globals().update(self.__dict__) does work, but would be a terrible practice in general.

argentum2f
– argentum2f

2020年03月17日 16:24:49 +00:00
Commented Mar 17, 2020 at 16:24
5

@WestCoastProjects I couldn't agree more. I believe in the principles outlined in "Clean Code" by Uncle Bob. And having "self." EVERYWHERE in my code DOES NOT make it any more readable or simple.

MickeyDickey on codidact.com
– MickeyDickey on codidact.com

2021年09月22日 17:11:34 +00:00
Commented Sep 22, 2021 at 17:11

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How to avoid explicit 'self' in Python?

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