meta.py

class A:
    def hallo(self):
        return "Hallo Welt"

def logger(obj, methodname):
    tmp_method = getattr(obj, methodname)
    def tmp_logger(*args):
        print("Open:", methodname)
        result = tmp_method(*args)
        print("Closing:", methodname)
        return result
    setattr(obj, methodname, tmp_logger)

a = A()
b = A()

logger(b, "hallo")

print("----------\nprint(a.hallo())")
print(a.hallo())
print("----------\nprint(b.hallo())")
print(b.hallo())
print("----------\nprint(a.hallo())")

logger(A, "hallo")

print(a.hallo())

# ----------
# print(a.hallo())
# Hallo Welt
# ----------
# print(b.hallo())
# Open: hallo
# Closing: hallo
# Hallo Welt
# ----------
# print(a.hallo())
# Open: hallo
# Closing: hallo
# Hallo Welt