ModExcel function

[ElmoGeeraerts]

I managed to write the ModExcel method so that value for the argument is also updated if you change a certain value for a certain key. However, if you call the method for one vendor but modify another, the value for the vendor you called the method for is updated. I raised the issue in my tutorial and warned against calling the method for one vendor but modify another. But I wanted to know if there is a quick and simple way to solve it.

[montesmariana]

Ok, there are several ways of adapting the code depending on what you want the actual purpose and scope of ModExcel to be, although I wouldn't say they are "quick and simple". My main thoughts would be: creating a static method (like a class attribute, but for a method) or having the index as an instance attribute instead of an argument. I added a third patch as quick and dirty solution for the time being.

The main problem you are having here is that your current ModExcel() method has two arguments that are supposed to identify a vendor, and nothing is enforcing them to identify the same vendor. These are self and Index. The solutions I offer discard one of these arguments.

Static method

Just like you can have class attributes that are attached to the class, not the instance (e.g. VendorData.CatTools), you can have methods that are attached to the class, not the instance. A crucial difference is that they do not take the self argument, but also you precede them with @staticmethod:

# vendor_data.py
@staticmethod
def ModExcel(Key, Index, NewValue):
   ....

This makes sense if you are not actually accessing properties of a specific instance. Then the function is called as VendorData.ModExcel(Key, Index, Newvalue) instead of having to attach it to an instance.
In your case, the problem is that you do use information from a specific instance to learn the name of the file to open...

Note that you could also have a class method, where you provide cls as an argument (instead of self), so that class attributes are still available (e.g. as cls.CatTools). You can learn more about this in this blogpost.

Index as instance attribute

An alternative would be that you don't provide the Index as an argument but that it is already set as an attribute of your instance. Either you have set it before or you obtain the information by finding the row in the Excel file.
Note that when you are reading the Excel file, you tend to turn it into a dictionary, but it might be easier to just read the Pandas dataframe:

• If you do some_vendor = ExcelRecordsDf.loc[0,:], you can then retrieve its name with some_vendor.Vendor.
• You can also retrieve the row that matches a given value like so: some_vendor = ExcelRecordsDf[ExcelRecordsDf.Vendor == 'Elmo Geeraerts']. From there you can obtain the right index too (some_vendor.index[0]).

Just validation

If (at this stage) any of those solutions seem too much work, you can simply deal with it with validation for the time being: before trying any modification, check in the Excel file that the index provided contains the data of the instance you are modifying, and if it doesn't, throw an error.