can't set attribute in class instance in Python

Question

I'm trying to create a instance of a class to test that the module I created is working properly.

Here is the module (fileWriter.py), the error appears to be in the init method:

class File(object):
'''process the data from a file'''

#fields
#fileName = name of file
#textData = data read from/written to file

#Constructor
def __init__(self, fileName = 'saved_data.txt', textData = ''):
    #Attributes
    self.fileName = fileName
    self.textData = textData

#Properties
@property #getter
def fileName(self):
    return self.__fileName

@fileName.setter #setter
def fileName(self, value):
    self.__fileName = value

@property #getter
def textData(self, value):
    self.__textData = value

#Methods
def saveData(self):
    '''appends data to file'''
    try:
        fileObj = open(self.fileName, 'a')
        fileObj.write(self.textData)
        fileObj.close()
    except Exception as e:
        print('You have the following error: ' + str(e))
    return('Data successfully saved to file.')

def toString(self):
    '''returns text data explicitly'''
    return self.fileName + ':' + self.textData

def __str__(self):
    '''returns text data implicitly'''
    return self.toString()

To test the class, I wrote the following test harness:

    import fileWriter

    import fileWriter

#test harness
processorObj = fileWriter.File()
processorObj.fileName = 'test.txt'
processorObj.textData = 'testing, 1, 2, 3...'
strMessage = processorObj.saveData()
print(strMessage)

if __name__ == '__main__':
    raise Exception('Don\'t run a module by itself!')

When I run the test file, I get the error:

File "testFileWriter.py", line 4, in processorObj = fileWriter.File() File "/Users/Haruka/Documents/python_class/Employees/fileWriter.py", line 19, in init self.textData = textData AttributeError: can't set attribute

I can't figure out what's wrong with self.textData = textData. Can anybody help?

Mark M · Accepted Answer · 2023-02-19 21:42:20Z

I'm not sure if you formatted your code after pasting, but there are a few typos:

def __init__(self, file_name = 'saved_data.txt', text_data = ''):
    #Attributes
    self.__file_name = file_name
    self.__text_data = text_data

and

@property #getter
def text_data(self):
    return self.__text_data

Later in test, you're also trying to set the text_data property without a setter in your example. You can add to your class:

@textData.setter
def text_data(self, value):
    self.__text_data = value

The more pythonic way to do some of the file io stuff is with a context.

def save_data(self):
    '''appends data to file'''

    with open(self.file_name, 'a') as f:
        f.write(self.text_data)
    return('Data successfully saved to file.')

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