Name Error: name 'Stockton' is not defined

[Pinokchu]

data = DataPortal(model=m)
    
data.load(filename="Dataframe2.xlsx", range='D2:D6', set='I')
data.load(filename="Dataframe2.xlsx", range='A2:A99', set='J')
data.load(filename="Dataframe2.xlsx", range='A1:B99', param='d', index='J')
data.load(filename="Dataframe2.xlsx", range='G1:L99', param='c', format='transposed_array')
data.load(filename="Dataframe2.xlsx", range='D1:E6' , param='b', index='I')
data.load(filename="Dataframe2.xlsx", range='N1:O6' , param='i', index='I')

data = {None: {
    'e' : {Stockton:325000, Rockwall:50000, Joliet:350000, Atlanta:450000, York:170000},
}}

m = m.create_instance(data)
m = m.create_instance(data)

After running it there is the following error code:

NameError Traceback (most recent call last)
<ipython-input-264-1e6fce871313> in <module>
9
10 data = {None: {
---> 11 'e' : {Stockton:325000, Rockwall:50000, Joliet:350000, Atlanta:450000, York:170000},
12 }}
13

NameError: name 'Stockton' is not defined

The numbers are maximum restrictions and the city names are places. If somebudy could help or give any advice I'd be grateful.