import re
p = r'm=(\w+)'
s = "2016-03-08 11:23:25 test_data:0317: m=string_I_want max_count: 17655, avg_size: 320, avg_rate: 165"
mObj = re.search(p, s)
if mObj:
print(mObj.group(1))
aW1wb3J0IHJlCnAgPSByJ209KFx3KyknCnMgPSAiMjAxNi0wMy0wOCAxMToyMzoyNSAgdGVzdF9kYXRhOjAzMTc6IG09c3RyaW5nX0lfd2FudCBtYXhfY291bnQ6IDE3NjU1LCBhdmdfc2l6ZTogMzIwLCBhdmdfcmF0ZTogMTY1IgptT2JqID0gcmUuc2VhcmNoKHAsIHMpCmlmIG1PYmo6CglwcmludChtT2JqLmdyb3VwKDEpKQ==