Splitting Python code into separate functions

Question

I am writing a large program, and I would like to break out functional chunks into other modules to make coding & maintenance easier.

---

main.py

---

#  Call Schedule Program -- v0.1a
#  Here we go ..

import tkinter as tk
import tkinter.font as font

from reporting import *             # bring in the stuff from reporting.py


def center_window_on_screen():
# This centres the window when it is not maximised.

    x_cord = int((screen_width / 2) - (width / 2))
    y_cord = int((screen_height / 2) - (height / 2))
    root.geometry(f"{width}x{height}+{x_cord}+{y_cord}")

<<snip!>>

def change_main_to_report():
# changes from main frame to schedule management frame

    reporting_frame.pack(fill='both', expand=1)
    main_frame.forget()


def change_report_to_main():
# changes from schedule management frame back to main frame
    main_frame.pack(fill='both', expand=1)
    reporting_frame.forget()

<<snip!>>

# ---------------< Begin the real work >---------------
# Let's set up the window ...

root = tk.Tk()
root.title("The Dreaded Call Schedule v0.1a")
root.configure(bg='lightyellow')

width, height = 800, 600
screen_width = root.winfo_screenwidth()
screen_height = root.winfo_screenheight()
center_window_on_screen()

# Here, we create frames which we will swap between 
main_frame = tk.Canvas(root, width=800, height=600)
file_maint_frame = tk.Canvas(root, width=800, height=600)
phys_maint_frame = tk.Canvas(root, width=800, height=600)
reporting_frame = tk.Canvas(root, width=800, height=600)        # setup reporting frame

# Let's create the fonts that we need.
font_large = font.Font(family='Candara',
                       size=24,
                       weight='bold')
font_small = font.Font(family='Candara',
                       size=12)

# ---------------< Main Frame >---------------
# The widgets needed for the Main frame.
# First, let's display the logo.

<<snip!>>

# ---------------< Reporting Frame >---------------
# The widgets needed for the File Maintenance frame.

setup_reporting_frame()         # this code got moved into reporting.py (below)


# ---------------< Open and Read data files >---------------

# Open the files and set those up
#  Physician, Special Characters, Calendar, Main Schedule

<<snip!>>


# ---------------< Main Routine >---------------
# 

main_frame.pack(fill='both', expand=1)

root.mainloop()

And below is Reporting.py

---

reporting.py

---

# ---------------< Reporting Frame >---------------
# The widgets needed for the reporting frame.

def setup_reporting_frame():

    reporting_frame = tk.Canvas(root, width=800, height=600)

    img_logo_report = tk.PhotoImage(file='logo.png')
    lbl_logo_report = tk.Label(reporting_frame, image=img_logo_report)
    lbl_logo_report.place(x=680, y=8)

# add a heading.
    lbl_heading_report = tk.Label(reporting_frame,
                            text='Reporting Menu',
                            font=font_large)
    lbl_heading_report.place(x=150, y=100)

# button for main availability
    btn_change_report_to_main_avail_rpt = tk.Button(reporting_frame,
                               font=font_small,
                               text='Main Availability',
                               command=change_report_to_main_avail_rpt)
    btn_change_report_to_main_avail_rpt.place(x=150, y=200)

# button for surgical avail
    btn_change_report_to_sx_avail_rpt = tk.Button(reporting_frame,
                               font=font_small,
                               text='Surgical Availability',
                               command=change_report_to_sx_avail_rpt)
    btn_change_report_to_sx_avail_rpt.place(x=350, y=200)

# button to generate main schedule
    btn_change_report_to_main_sched_rpt = tk.Button(reporting_frame,
                               font=font_small,
                               text='Main Call Schedule',
                               command=change_report_to_main_sched_rpt)
    btn_change_report_to_main_sched_rpt.place(x=150, y=250)

# button to generate surgical schedule
    btn_change_report_to_sx_sched_rpt = tk.Button(reporting_frame,
                               font=font_small,
                               text='Surgical Schedule',
                               command=change_report_to_sx_sched_rpt)
    btn_change_report_to_sx_sched_rpt.place(x=350, y=250)

# button to swap back to the main frame.
    btn_change_to_main = tk.Button(reporting_frame,
                               font=font_small,
                               text='Exit',
                               command=change_report_to_main)
    btn_change_to_main.place(x=150, y=350)

    reporting_frame.create_line(750, 300, 700, 400, width=3, fill='aqua')

When I try running this, I get an error saying that tkinter isn't defined. If I put in a definition for tk, the error moves to saying 'reporting_frame' isn't defined. After that it moves to the fonts and so on.

I have browsed around and found similar solutions, but they invariably lead to defining things as a Class. I honestly don't see how this lends itself to being defined as a class.

What I'm looking for is how to set this up so that I have the Main, and I include a bunch of other modules. I suspect I'm missing something basic here, but I don't see it. I was under the impression that the files would be compiled, and then the linker would resolve name problems.

For reference, I'm using the latest version of Python, and PyCharm v2021.3

If anyone can help, that would be greatly appreciated.

Thanks muchly.

thomas