Python:IndexError: list index out of range in python - python-2.7

Question

So, i'm just a noob when it comes to programming especially python. I have a list holding all the variable names that i'm using in my program:
dList=['market_a','market_b','market_c','market_d','market_e','market_f','market_g']
What i want to do is remove all these objects from memory i.e., this is what i believe needs to be done:
del market_a,market_b,market_c,market_d,market_e,market_f,market_g
market_a=market_b=market_c=market_d=market_e=market_f=market_g= None
I was trying to del the objects by doing something like this:
for index in (len(dList):
del dList[index]
But i'm getting this error.
IndexError: list index out of range
Can somebody please help me with this? Also can somebody please tell me how i can do market_a=market_b=market_c=market_d=market_e=market_f=market_g= Nonefrom dList?
Thanks in advance.

Answer 1

I am not recommending that you do this (see below for a dictionary based solution), however, you can use the exec statement to assign None to the variables:
dList = ['market_a', 'market_b', 'market_c', 'market_d', 'market_e', 'market_f', 'market_g']
for var in dList:
exec '{} = None'.format(var)
You can also explicitly call del on the variable:
for var in dList:
exec 'del {}'.format(var)
# exec '{} = None'.format(var)
although this is not usually required because, if the object to which a variable name was bound has no other references to it, rebinding the variable name results in the original object being eligible for garbage collection and so it will eventually be removed from memory.
In general it makes little sense to store a list of variable names: if the variables are static, that is, known to your code at "compile" time, then you already know what they are called and can simply refer to them by name in your code.
If the variables are dynamic then you'd be better off using a dictionary to associate the names with values. Treat the entries in the dictionary as your variables.
markets = {'a': 1, 'b': 2, 'c': 3, 'd': 4, 'e': 5, 'f': 6, 'g': 7}
# to access a "variable"
>>> markets['a']
1
# to modify a "variable"
>>> markets['a'] += 100
>>> markets['a']
101
To delete them all you can simply delete the dictionary:
del markets
or rebind it to an empty dictionary:
markets = {}
Assuming that there is no other reference to the objects stored as values in the dictionary, this will make these objects available for garbage collection, effectively deleting them from memory.
Or you can delete specific keys:
# to delete a specific "variable"
del markets['a']
Unless it is required by your algorithms there's no need to assign None.

Answer 2

As you delete your array is getting smaller, therefore the index is no longer correct.
You can try this:
while dList:
del dList[0]
Just a note when the array is empty, it will evaluate to False.

Answer 3

As mentioned above as you remove items the array gets smaller so a for loop is probably not the best solution. To me it looks like you are trying to accomplish 2 tasks: shrink the array and physically delete the variables:
while dList:
var = dList.pop(0)
exec('del {0}'.format(var))
Consider using the pop() method which will shrink your array and then using the exec() method to delete the variable from memory by passing in the variable name and instead of deleting the string deleting the actual variable instance.