Python: loop over consecutive characters?

In Python (specifically Python 3.0 but I don't think it matters), how do I easily write a loop over a sequence of characters having consecutive character codes? I want to do something like this pseudocode:

for Ch from 'a' to 'z' inclusive: #
    f(Ch)

Example: how about a nice "pythonic" version of the following?

def Pangram(Str):
    ''' Returns True if Str contains the whole alphabet, else False '''
    for Ch from 'a' to 'z' inclusive: #
        M[Ch] = False
    for J in range(len(Str)):
        Ch = lower(Str[J])
        if 'a' <= Ch <= 'z':
            M[Ch] = True
    return reduce(and, M['a'] to M['z'] inclusive) #

The lines marked # are pseudocode. Of course reduce() is real Python!

Dear wizards (specially old, gray-bearded wizards), perhaps you can tell that my favorite language used to be Pascal.