Technical question about the code in 3.75

[Angelo]

Hello,
I am trying to understand how gam.py version 3.75 works.

i see line 258 defines
GC_Values = {}

i see line 214 & 215
# Path to oauth2.txt
GC_OAUTH2_TXT = u'oauth2_txt'

In Function def getClientAPIversionHttpService(api):
i see line 2607 defined
storage = oauth2client.file.Storage(GC_Values[GC_OAUTH2_TXT])

Question: Since GC_Values is a dictionary, so referencing GC_Values[GC_OAUTH2_TXT]
is the value of whatever is paired with key u'oauth2.txt' correct ?
If i am correct when/where does the code assign a value to the key ?

-ALF