dictionary – Passing of the optional argument in a function

I have a question regarding the transmission of default / optional arguments to a function. I try to read the values ​​of a dictionary that contains both keys and other (nested) codes. I've tried the "arg_A =" but it does not work with the way I'm looking for the value dict inside the function / I pass the wrong argument by default. I've included the short code below (I'm trying to write a graphical interface that's why the occurance "tkvar"):

Class parameters:
def __init __ (auto):
print ("Start sending the test")

def ChangeEntry (self, testdict, nested_dict = None, key, value):

print (testdict[nested_dict][key])

def GetTestName ():
settings = Settings ()

testfile = listOfTests.get (tkvartest.get ())

with tempfile.TemporaryFile () as tmp:

if (testfile == None):
print ("Choose the test you want to download")
testDict = open ("../Templates/" + str (test file) + ".json")
testdata = json.load (testDict)
settings.ChangeEntry (testdata, 1, & # 39; entryInDict & # 39 ;, somevalueToReplace TheCurrentOne & # 39;)

I do not see how to use args or kwargs with that. Can any one enlighten us about this?