Daily Add/Del Git Log Analysis
I would apply the following improvements:


use collections.defaultdict to count down the number of added and deleted lines separately. This would help to improve the counting logic and avoid having to check for the old date at all
use any() to check for the excluded wildcards
unpack args into added, deleted lines and a filename 
switch to gitpython from subprocess 


The new version of the code:

from collections import defaultdict
from datetime import datetime
from fnmatch import fnmatch

import git


EXCLUDED_WILDCARDS = ['*.eps', '*.CSV', '*jquery*']


def chomp_int(val):
    try:
        return int(val)
    except ValueError:
        return 0


repo = git.Repo(".")
git_log = repo.git.log(numstat=True, pretty="%at").encode("utf-8")

added, deleted = defaultdict(int), defaultdict(int)

for line in git_log.splitlines():
    args = line.decode('utf8').rstrip().split()

    if len(args) == 1:
        date = datetime.fromtimestamp(int(args[0])).date()
    elif len(args) &gt;= 3:
        added_lines, deleted_lines, filename = args

        # Don't count changesets for excluded file types
        if any(fnmatch(filename, wildcard) for wildcard in EXCLUDED_WILDCARDS):
            continue

        added[date] += chomp_int(added_lines)
        deleted[date] += chomp_int(deleted_lines)

for date, added_lines in added.items():
    print(date, added_lines, deleted[date])