understanding self

Colin J. Williams cjw at sympatico.ca
Thu Jul 8 13:47:57 CEST 2004



Jeff Shannon wrote:
> bruce stockwell wrote:
> 
>> Using 'self' in classes seems pretty straight forward. My curiosity is 
>> why I have to use it. Shouldn't it be implied?
> 
> 
> The problem is that an implied 'self' is harder to read than an explicit 
> 'self', and also opens the door for ambiguity when an instance attribute 
> has the same name as a global or builtin attribute.
> 
> Let's look at an example in a hypothetical Python variant where 'self' 
> is implied --
> 
> class eye:
>    def open(which):
>        # do stuff here
> 
>    def close(which):
>        # do stuff here
> 
>    def blink(which):
>        if closed:
>            open(which)
>            close(which)
>        else:
>            close(which)
>            open(which)
> 
> e = eye()
> e.blink('right')
> 
> But wait -- open() is an obsolete built-in function for opening a file.  
> Which should eye.blink() do -- open and close the right eye, or open a 
> file with the name of 'right' ??  If it's the former, then what do you 
> do if you *want* to open that file?  If it's the latter, then what 
> happens when the next version of Python comes along and open() has been 
> removed from built-ins?
> 
> Even without these namespace conflicts, it's difficult when you're 
> reading a long method and see a call to "make_thingumbob()" -- where do 
> you look to see what that does?  It might be another method of that 
> class, or it might be a global (or even built-in) function.  It then 
> requires extra thought and search-time to figure out the intent.
> 
> One of the design principles of Python is that ease of *reading* is more 
> important than ease of *writing*.  It's worth a few extra keystrokes if 
> it will save you a second or two of time when reading unfamiliar code -- 
> because most code is only written once, but read *many* times.
> 
> Jeff Shannon
> Technician/Programmer
> Credit International
> 
I'm sure this issue has been flogged before.

Couldn't both clarity and simplicity be achieved by replacing the 
"self." with ".".  self is not normally at the left of an assignment and 
the self would not need to appear in the method signature.

Version 3 pehaps?

Colin W.




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