object.attribute vs. object.getAttribute()

Roy Smith roy at panix.com
Tue Sep 16 02:29:10 CEST 2003

For the past 6-8 months, I've spent most of my time writing C++ and a 
little bit of Java.  Both of these languages support and encourage the 
use of private data and explicit accessor functions, i.e. instead of 
writing x = foo.bar, you write x = foo.getBar().  Now that I'm back to 
writing Python, I find myself in a quandry.

Historically, I've always avoided accessor functions and just reached 
directly into objects to get the value of their attributes.  Since 
Python doesn't have private data, there really isn't much advantage to 
writing accessors, but somehow I'm now finding that it just feels wrong 
not to.  I'm not sure if this feeling is just a C++/Java-ism that will 
cure itself with time, or if perhaps it really does make sense and I 
should change the way I code.

On the plus side, accessors/mutators give me:

1) Implicit documentation of which attributes I intended to be part of 
an object's externally visible state (accessors).
2) Hooks to do data checking or invarient assertions (mutators).
3) Decoupling classes by hiding the details of data structures.
4) Vague feeling that I'm doing a good thing by being more in line with 
mainstream OO practices :-)

On the minus side:

1) More typing (which implies more reading, which I think reduces the 
readability of the finished product).
2) Need to write (and test) all those silly little functions.
3) Performance hit due to function call overhead.
4) Only the appearance of private data (modulo some slots hackery).
5) Code is harder to change (adding functionality means going back and 
adding more slots).
6) Vague feeling that I'm dirtying myself by letting C++ and Java change 
my Python coding habits :-)


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