Python Pandas Attributeerror: 'Str' Object Has No Attribute 'Isin'

First question here. I am attempting to use pandas to create a new column ('zone') in my dataframe based on the values of other columns in my dataframe. I am using address data.

Here is some sample data, my real dataset has 25k rows. sample_df:

Shipping City   Shipping Zip    State   DISTRICT NAME
Garden City 11530   NY  NEW YORK 2
San Francisco   94117   CA  CALIFORNIA 1
Frisco  75036   TX  TEXAS 1
Las Vegas   89139   NV  NV-UT
Beverly Hills   90212   CA  CALIFORNIA 5

here is sample criteria for the new column:

In general if in mid west or east coast I can use state to assign the zone. for NY: zone_8 TX: zone_6 For California, I want to split into 3 different zones: NorCal, Socal, and central Cal -which will also include Las Vegas and Phoenix. I can use the given 'District Name' column to divide CA only. for special cities I can use 'Shipping City'. he rest of the sample expected results are below:

Expected Result:

    Shipping City   | Shipping Zip  | State | DISTRICT NAME | Zone  
-----           | -----         | ----- | -----         | ----- 
Garden City | 11530         | NY    | NEW YORK 2    | zone_8    
San Francisco   | 94117         | CA    | CALIFORNIA 1  | zone_3    
Frisco          | 75036         | TX    | TEXAS 1       | zone_6    
Las Vegas       | 89139         | NV    | NV-UT         | zone_2    
Beverly Hills   | 90212         | CA    | CALIFORNIA 5  | zone_2    

I created lists for my expected values:

zone8_state = ['ME', 'NH', 'VT', 'MA', 'RI', 'CT', 'AA', 'HI', 'NY', 'PA', 'NJ', 'MD', 'DE',          'WV', 'OH', 'VA', 'NC', 'SC', 'GA', 'FL', 'MI']
zone7_state = ['KY', 'IN', 'IL', 'WI', 'MN', 'TN', 'AL','LA', 'MS', 'AR']
zone6_state = ['IA', 'MO', 'ND', 'SD', 'NE', 'KS', 'OK', 'TX']
zone5_state = ['MT', 'WV', 'CO', 'NM', 'ID', 'WA', 'OR']
zone4_state = ['UT', 'NV', 'AZ']
norcal = ['CALIFORNIA 1', 'CALIFORNIA 2']
socal = ['CALIFORNIA 4', 'CALIFORNIA 5']
zone3_city = ['CALIFORNIA 3', 'Las Vegas', 'Phoenix']

Then I made a function:

def get_zones(sample_df):
    if sample_df['State'].isin(zone8_state):
        return 'zone_8'
    elif sample_df['State'].isin(zone7_state):
        return 'zone_7'
    elif sample_df['State'].isin(zone6_state):
        return 'zone_6'
    elif sample_df['State'].isin(zone5_state):
        return 'zone_5'
    elif sample_df['State'].isin(zone4_state) | sample_df['DISTRICT NAME'].isin(norcal):
        return 'zone_4'
    elif sample_df['DISTRICT NAME'].isin(zone3_city) | sample_df['Shipping City'].isin(zone3_city):
        return 'zone_3'
    elif sample_df['DISTRICT NAME'].isin(socal):
        return 'zone_2'
    else:
        return 'check the record'

THen I applied the function to my df:

sample_df['zone'] = sample_df.apply(get_zones, axis=1)

after I apply though, I get this:

AttributeError: 'str' object has no attribute 'isin'

can you please help me to get my function to work correctly? I also tried using 'contains' instead of 'isin' but also get a similar Attribute error. Thanks.