I'm new to python and need to create a list with a negative index but have not been successful so far.

I'm using this code:

a = []
for i in xrange( -20, 0, -1 ):a[i] = -(i)log.info('a[{i}]={v}'.format(i=i, v=a[i]))
else:log.info('end')

and getting the log output as

end

Incidentally I'm using a site call quantopian so the log.info is from their infrastructure and just print out the output into a web console.

What am I doing wrong?

Thanks in advance for your help.

If you are using Quantopian, it is advisable that you become familiar with numpy and pandas. For example:

>>> import numpy as np 
>>> -1*np.arange(20)array([  0,  -1,  -2,  -3,  -4,  -5,  -6,  -7,  -8,  -9, -10, -11, -12,-13, -14, -15, -16, -17, -18, -19])

Then you will have a[1]==-1, a[5]==-5, etc.