Calling an attribute defined in a method from another method in data science (python)

I’m learning object oriented programing in a data science context.

I want to understand what good practice is in terms of writing methods within a class that relate to one another.

When I run my code:

import pandas as pd 
pd.options.mode.chained_assignment = None  

class MyData:
    def __init__(self, file_path):
        self.file_path = file_path

def prepper_fun(self):
    '''Reads in an excel sheet, gets rid of missing values and sets datatype to numerical'''
    df = pd.read_excel(self.file_path) 
    df = df.dropna()                    
    df = df.apply(pd.to_numeric) 
    self.df = df
    return(df)

def quality_fun(self):
   '''Checks if any value in any column is more than 10. If it is, the value is replaced with
   a warning 'check the original data value'.'''
    for col in self.df.columns:
        for row in self.df.index:                                             
            if self.df[col][row] > 10:       
                self.df[col][row] = str('check original data value') 
    return(self.df) 

data = MyData('https://archive.ics.uci.edu/ml/machine-learning-databases/00429/Cryotherapy.xlsx')
print(data.prepper_fun())
print(data.quality_fun())

I get the following output (only part of the output is shown due to space constrains):

     sex  age   Time  
0     1   35  12.00             
1     1   29   7.00               
2     1   50   8.00                
3     1   32  11.75                
4     1   67   9.25                         
..  ...  ...    ...       


     sex                        age                       Time 
0     1  check original data value  check original data value                  
1     1  check original data value                          7                  
2     1  check original data value                          8                  
3     1  check original data value  check original data value               
4     1  check original data value                       9.25 
..  ...                        ...                        ...

I am happy with the output generated by each method.

But if I try to call print(data.quality_fun()) without first calling print(data.prepper_fun()), I get an error AttributeError: 'MyData' object has no attribute 'df'.

Being new to objected oriented programming, I am wondering if it is considered good practice to structure things like this, or if there is some other way of doing it.

Thanks for any help!

Answer

Make sure you have the df before you use it.

class MyData:
    def __init__(self, file_path):
        self.file_path = file_path
        self.df = None
    def quality_fun():
       if self.df is None:
          self.prepper_fun()
       # rest of the code