CSV parsing program that creates distinct header rows with transaction rows underneath
Don't reuse names for multiple purposes

Before this line, reader is a DictReader,
after this line it's a list:


    reader = sorted(reader, key=lambda key: (key['PEOPLE_ID'], 
                                             key['DON_DATE']))



This can be confusing. It would be better to name the result something else.
And it gets worse: this new reader reader is passed to create_header_list and mapData as parameter named "dict_obj",
which further adds to the confusion.

Simplify set creation

This function essentially creates a set:


def create_header_list(dict_obj):
    p_id_list = []
    for row in dict_obj:
        if (row['PEOPLE_ID'], row['DON_DATE']) not in p_id_list:
            p_id_list.append((row['PEOPLE_ID'], row['DON_DATE']))
    return p_id_list



The not in check is inefficient, because it's an \$O(n)\$ operation.

It would be simpler and more efficient to use a set:

def create_header_list(dict_obj):
    p_id_set = set()
    for row in dict_obj:
        p_id_set.add((row['PEOPLE_ID'], row['DON_DATE']))
    return p_id_set


Or even:

def create_header_list(dict_obj):
    return set([(row['PEOPLE_ID'], row['DON_DATE']) for row in dict_obj])


If the ordering of the elements is important,
then instead of a set, you can use an OrderedDict,
as suggested by this post.

Running Python scripts

Not all systems have Python at /use/bin/python. The recommended shebang for Python scripts:

#!/usr/bin/env python


Follow PEP8

PEP8 is the coding style guide for Python.
Among other things,
it recommends using snake_case for variable and function names.
Several functions violate that.

Even if you disagree with a specific naming convention,
it's a universal violation of good naming practices to mix two kinds of naming styles in the same program, such as create_header_list and mapData.