import os
import os.path

alphanum = "abcde fghij klmno pqrst uvwxy z ABCDE FGHIJ KLMNO PQRST UVWXY Z 0123456789 -_= () !$@#%.,~"
d = "/path/to/your/folder"
for fn in os.listdir(d):
    rename_flag = False
    altn = ""
    for c in fn:

        if c in alphanum:
            altn += c
        else:
            altn += "_"+str(ord(c))
            rename_flag = True

    if rename_flag:
        os.rename(os.path.join(d,fn), os.path.join(d,altn))