How to return a pandas Series from an inner function

Question

This script is a simplified version of what I have as its too long to put here. I have tried to include all necessary information.

class data():

    def collect_data(self):
        def reader(n):
            self.df[n] = self.join_data(self.EO[n].real)
        # for i in (1, 2, 4, 6): reader(i)

    def join_data(self, func1)
        do stuff
        return self.df # is a Series

    def data_excel(self)
        self.df[1].to_excel(......) #line 1
        self.df[2].to_excel(......)
        self.df[4].to_excel(......)
        self.df[6].to_excel(......)

#on line 1
AttributeError: 'str' object has no attribute 'to_excel'

The Series contains chunks of "strings and numeric" data where each chunk starts with row index 0.

print(dfEO_RI.head(1).to_dict())

{0: '*amplitude'}
{0: '*amplitude'}
{0: '*amplitude'}
{0: '*amplitude'}

The function join_data successfully returns a Series but I dont know how to correctly pass it through the function collect_data and subsequently to function data_excel

Desired Output

4 Series data output to excel