Variable Pointer to Dynamically Changing List Entry

[physicslad]

Hi,

I have in my program a list of lists of variables. These variables change as the program runs. I would like to be able to link meaningful names to the variables. So, say I have a list of quantities of different coins in my possession

 
myChange = [0, 0, 0, 1]

where the entries are the quantities of pennies, nickels, dimes, and quarters I have, respectively. Can I assign variable names to the entries so that if, in the course of my program, it simulates a purchase for 5 cents-

myChange [3] = myChange [3] - 1
myChange [2] = myChange [2] + 2

I can say

print quarters
print dimes

And get the following output?

0
2

Thanks for the help; sorry if my terminology is bad as I am new to programming!

[bartonc]

Hi,

I have in my program a list of lists of variables. These variables change as the program runs. I would like to be able to link meaningful names to the variables. So, say I have a list of quantities of different coins in my possession

 
myChange = [0, 0, 0, 1]

where the entries are the quantities of pennies, nickels, dimes, and quarters I have, respectively. Can I assign variable names to the entries so that if, in the course of my program, it simulates a purchase for 5 cents-

myChange [3] = myChange [3] - 1
myChange [2] = myChange [2] + 2

I can say

print quarters
print dimes

And get the following output?

0
2

Thanks for the help; sorry if my terminology is bad as I am new to programming!

Your terminology (and use of this site) is excellent for a beginner!

You could achive 100% of your goal (getting a reference to an array item) using an extension called scipy. A 99% solution with native lists requires that you unpack the list each time you want to use it. It's a technique that I use often:[CODE=python]
>>> aList = [1, 2, 3, 4]
>>> pennies, nickles, dimes, quarters = aList
>>> quarters
4
>>> [/CODE]

[bvdet]

You may consider using a class for your program. This is a start:[code=Python]class myChange(object ):

def __init__(self, penny=0, nickel=0, dime=0, quarter=0):
self.penny = penny
self.nickel = nickel
self.dime = dime
self.quarter = quarter
self.data = [penny,nickel,di me,quarter]
self.__init = 1

def __getitem__(sel f, i):
return self.data[i]

def __setitem__(sel f, i, value):
try:
object.__setatt r__(self, {0:'penny',1:'n ickel',2:'dime' ,3:'quarter'}[i], int(value))
object.__setatt r__(self, 'data', [int(self.penny) , int(self.nickel ), int(self.dime), int(self.quarte r)])
except KeyError:
raise IndexError, "Index argument out of range in '%s' __setitem__" % (type(self).__n ame__)
except ValueError:
raise ValueError, "Invalid literal in '%s' __setitem__" % (type(self).__n ame__)

def __setattr__(sel f, name, value):
if not self.__dict__.h as_key('_myChan ge__init'):
return object.__setatt r__(self, name, value)
elif self.__dict__.h as_key(name):
object.__setatt r__(self, name, value)
object.__setatt r__(self, 'data', [int(self.penny) , int(self.nickel ), int(self.dime), int(self.quarte r)])
else:
raise AttributeError, "'%s' object has no attribute '%s'" % (type(self).__n ame__, name)[/code]Here is some interaction:[code=Python]>>> myChange(6,4,7, 2)
<__main__.myCha nge object at 0x00F972D0>
>>> chg = myChange(6,4,7, 2)
>>> chg.penny
6
>>> chg.penny = 12
>>> chg.data
[12, 4, 7, 2]
>>> chg.quarter += 7
>>> chg.quarter
9
>>> chg.data
[12, 4, 7, 9]
>>> chg[3]=3
>>> chg.quarter
3
>>> chg[3]
3
>>> chg[4]
Traceback (most recent call last):
File "<interacti ve input>", line 1, in ?
File "C:\SDS2_7.0\ma cro\Work In Progress\myChan ge.py", line 13, in __getitem__
return self.data[i]
IndexError: list index out of range
>>> [/code]