Prepend and append to your source files

gistfile1.txt

import os
for root, dirs, files in os.walk("."):
    for file in files:
        if file.endswith(".py"):
            my_path = os.path.join(root, file)
            # sed does not work on truly empty file
            os.system("sed -i '1s;^;import os\\nos.system(\"echo DEBUT \" + os.path.abspath(__file__) + \" >> /tmp/montest\")\\n;' " + my_path)
            os.system("echo '\\nos.system(\"echo FIN \" + os.path.abspath(__file__) + \" >> /tmp/montest\")' >> " + my_path)

# A variant to avoid complicated escaping
in . add two files:

to_prepend.supertxt
-------------------
import os
os.system("echo DEBUT " + os.path.abspath(__file__) + " >> /tmp/montest")

-------------------

to_append.supertxt mind the leading newline :)
------------------

os.system("echo FIN " + os.path.abspath(__file__) + " >> /tmp/montest")

------------------

import os
for root, dirs, files in os.walk("."):
    for file in files:
        if file.endswith(".py"):
            my_path = os.path.join(root, file)
            os.system("cat ./to_prepend.supertxt " + my_path + " > tmp.supertxt && mv tmp.supertxt " + my_path)
            os.system("cat ./to_append.supertxt >> " + my_path)