Index Error, can't understand why.

[Diamond]

Hello!
I am getting an IndexError, and not sure why? My goal is to print out the higher numeric list element.

def mag(var):
    pos=0
    mob=1
    while pos < len(var):
        if var[pos]<var[mob]: 
            pos = mob
            mob += 1
        else:
            mob += 1
    print pos

it returns this error:

Error:
line 5, in mag
    if var[pos]<var[mob]:
IndexError: list index out of range

i have already tried to change the code several times but the result is the same, may you help me to understand the problem?
Thanks a lot!