Q:

Unable to access sheet in a method? 

Unresolved reference 'sheet' error happens. 
The code I have tried is below:
class User():
    def __init__(self, sheet_path):
        self.file = glob.glob(sheet_path)
        self.construction_area ={}

    def read(self):
        for x in self.file:
            if "$" not in x:
                book = xlrd.open_workbook(x)
                sheet = book.sheet_by_index(0)
                cells = [('user_id', 0, 9),
                             ('name', 4, 0),
                             ('age', 4, 1),]
　　　　　　　　　　・
　　　　　　　　　　・
　　　def save(self):
　　　　　　　　　　・
　　　　　　　　　　・
            for row_index in range(7, sheet.nrows):
                row = sheet.row_values(row_index)
　　　　　　　　　　・
　　　　　　　　　　・
x = User('./data/*.xlsx')
x.read()
x.save()

In sheet of save method the error happens. I added self in front of sheet, but AttributeError: 'User' object has no attribute 'sheet' error happens. 
Why can't I access 'sheet' ?  Is making instance not enough ?  How can I fix this? 

A:

In python, to access to an instance member, you have to specify the instance, by using the classical self keyword from inside the instance. 
Your sheet variable, is locally created in the read method, but only locally, it is never attached to the current instance of User. 
If you need to save these sheet (and it looks like this is what you want ;) ), you'll have to use the self.sheet everywhere (and moreover, declare it in the __init__ method)
class User():
    def __init__(self, sheet_path):
        self.file = glob.glob(sheet_path)
        self.construction_area ={}
        self.sheet = None

    def read(self):
        for x in self.file:
            if "$" not in x:
                book = xlrd.open_workbook(x)
                self.sheet = book.sheet_by_index(0)
                cells = [('user_id', 0, 9),
                         ('name', 4, 0),
                         ('age', 4, 1),]

    def save(self):
        for row_index in range(7, sheet.nrows):
            row = self.sheet.row_values(row_index)

