Python win32com SendKeys fail

I've tried to do button press test and every time I do it, it fails somewhere. There is always place where there are two (or more) lower case letters next to one another or two upper case. Why is that?

import win32com.client

shell = win32com.client.Dispatch("WScript.Shell")
shell.Run("notepad")
shell.AppActivate("Notepad")


def a():
    shell.SendKeys("{a}", 0)


def A():
    shell.SendKeys("{A}", 0)


def b():
    shell.SendKeys("{b}", 0)


def B():
    shell.SendKeys("{B}", 0)


def c():
    shell.SendKeys("{c}", 0)


def C():
    shell.SendKeys("{C}", 0)


def d():
    shell.SendKeys("{d}", 0)


def D():
    shell.SendKeys("{D}", 0)


def e():
    shell.SendKeys("{e}", 0)


def E():
    shell.SendKeys("{E}", 0)


def f():
    shell.SendKeys("{f}", 0)


def F():
    shell.SendKeys("{F}", 0)


def g():
    shell.SendKeys("{g}", 0)


def G():
    shell.SendKeys("{G}", 0)


def h():
    shell.SendKeys("{h}", 0)


def H():
    shell.SendKeys("{H}", 0)


def i():
    shell.SendKeys("{i}", 0)


def I():
    shell.SendKeys("{I}", 0)


def j():
    shell.SendKeys("{j}", 0)


def J():
    shell.SendKeys("{J}", 0)


def k():
    shell.SendKeys("{k}", 0)


def K():
    shell.SendKeys("{K}", 0)


def l():
    shell.SendKeys("{l}", 0)


def L():
    shell.SendKeys("{L}", 0)


def m():
    shell.SendKeys("{m}", 0)


def M():
    shell.SendKeys("{M}", 0)


def n():
    shell.SendKeys("{n}", 0)


def N():
    shell.SendKeys("{N}", 0)


def o():
    shell.SendKeys("{o}", 0)


def O():
    shell.SendKeys("{O}", 0)


def p():
    shell.SendKeys("{p}", 0)


def P():
    shell.SendKeys("{P}", 0)


def q():
    shell.SendKeys("{q}", 0)


def Q():
    shell.SendKeys("{Q}", 0)


def r():
    shell.SendKeys("{r}", 0)


def R():
    shell.SendKeys("{R}", 0)


def s():
    shell.SendKeys("{s}", 0)


def S():
    shell.SendKeys("{S}", 0)


def t():
    shell.SendKeys("{t}", 0)


def T():
    shell.SendKeys("{T}", 0)


def u():
    shell.SendKeys("{u}", 0)


def U():
    shell.SendKeys("{U}", 0)


def w():
    shell.SendKeys("{w}", 0)


def W():
    shell.SendKeys("{W}", 0)


def x():
    shell.SendKeys("{x}", 0)


def X():
    shell.SendKeys("{X}", 0)


def y():
    shell.SendKeys("{y}", 0)


def Y():
    shell.SendKeys("{Y}", 0)


def z():
    shell.SendKeys("{z}", 0)


def Z():
    shell.SendKeys("{Z}", 0)


def enter():
    shell.SendKeys("{ENTER}", 0)

a(), A(), b(), B(), c(), C(), d(), D(), e(), E(), f(), F(), g(), G(), h(), H(), i(), I(), j(), J(), k(), K(),
l(), L(), m(), M(), n(), N(), o(), O(), p(), P(), q(), Q(), r(), R(), s(), S(), t(), T(), u(), U(), w(), W(),
x(), X(), y(), Y(), z(), Z(), enter(),

Expected output: "aAbBcCdDeEfFgGhHiIjJkKlLmMnNoOpPqQrRsStTuUwWxXyYzZ"