While building a new class object in python, I want to be able to create a default value based on the instance name of the class without passing in an extra argument. How can I accomplish this? Here's the basic pseudo-code I'm trying for:
class SomeObject():
defined_name = u""
def __init__(self, def_name=None):
if def_name == None:
def_name = u"%s" % (<INSTANCE NAME>)
self.defined_name = def_name
ThisObject = SomeObject()
print ThisObject.defined_name # Should print "ThisObject"
Well, there is almost a way to do it:
#!/usr/bin/env python
import traceback
class SomeObject():
def __init__(self, def_name=None):
if def_name == None:
(filename,line_number,function_name,text)=traceback.extract_stack()[-2]
def_name = text[:text.find('=')].strip()
self.defined_name = def_name
ThisObject = SomeObject()
print ThisObject.defined_name
# ThisObject
The traceback module allows you to peek at the code used to call SomeObject().
With a little string wrangling, text[:text.find('=')].strip()
you can
guess what the def_name should be.
However, this hack is brittle. For example, this doesn't work so well:
ThisObject,ThatObject = SomeObject(),SomeObject()
print ThisObject.defined_name
# ThisObject,ThatObject
print ThatObject.defined_name
# ThisObject,ThatObject
So if you were to use this hack, you have to bear in mind that you must call SomeObject() using simple python statement:
ThisObject = SomeObject()
By the way, as a further example of using traceback, if you define
def pv(var):
# stack is a list of 4-tuples: (filename, line number, function name, text)
# see http://docs.python.org/library/traceback.html#module-traceback
#
(filename,line_number,function_name,text)=traceback.extract_stack()[-2]
# ('x_traceback.py', 18, 'f', 'print_var(y)')
print('%s: %s'%(text[text.find('(')+1:-1],var))
then you can call
x=3.14
pv(x)
# x: 3.14
to print both the variable name and its value.