How do I use TKinter to select two excel files as keep them as files?

I am using some stock TKInter code to select two separate Excel/csv files:

import tkinter as tk
import tkinter.filedialog as fd

root = tk.Tk()
file_1 = fd.askopenfilenames(parent=root, title='Choose a file')
file_2 = fd.askopenfilenames(parent=root, title='Choose a file')

What I want to do is to select two csv/Excel files and then compare them using the following code:

import pandas as pd

def cleanup():

    file_1 = pd.read_excel(excel_file, sheet_name="***")
    file_2 = pd.read_excel(excel_file, sheet_name="***")

    df = pd.merge(
    left=file_1,
    right=file_2,
    left_on="User Name",
    right_on = "ExternalID",
    how = "right")
    matched = df.to_csv("matched.csv", index=False)
    return matched

The error I get is the following: "TypeError: Can only merge Series or DataFrame objects, a <class 'tuple'> was passed." How can I use TkInter to select the file and treat it as a Dataframe converted from excel/csv?

fd.askopenfilenames returns a tuple of file names, since users can select multiple files in one dialog.

# Note the trailing comma to extract the a single path.
file_1, = fd.askopenfilenames(parent=root, title='Choose a file')
file_2, = fd.askopenfilenames(parent=root, title='Choose a file')

# Or use fd.askopenfilename (note the singular "name").
file_1 = fd.askopenfilename(parent=root, title='Choose a file')
file_2 = fd.askopenfilename(parent=root, title='Choose a file')

excel_1 = pd.read_excel(file_1, sheet_name="***")
excel_2 = pd.read_excel(file_2, sheet_name="***")

df = pd.merge(left=excel_1, right=excel_2, ...)

Also note that your cleanup method is parsing the same file twice:

file_1 = pd.read_excel(excel_file, sheet_name="***")
file_2 = pd.read_excel(excel_file, sheet_name="***")
#                      ^^^^^^^^^^

BoppreH gets to the heart of the issue; the file dialog returns a tuple of file names, not the files themselves.

If your files are in the same folder, another option is to use this code and select both files from the same dialog. Whichever you click first will become file_1.

import tkinter as tk
import tkinter.filedialog as fd
import pandas as pd

root = tk.Tk()
file_names = fd.askopenfilenames(parent=root, title='Choose two files')

def cleanup():

    file_1 = pd.read_excel(file_names[0], sheet_name="***")
    file_2 = pd.read_excel(file_names[1], sheet_name="***")

    df = pd.merge(
        left=file_1,
        right=file_2,
        left_on="User Name",
        right_on = "ExternalID",
        how = "right")
    matched = df.to_csv("matched.csv", index=False)
    return matched

print(cleanup())