I am not aware of any internal tkinter method to check if a button is pressed.

However you could connect the Button with a function that changes the value of a global variable, like in the following:

from Tkinter import *

master = Tk()

def callback():
    global buttonClicked
    buttonClicked = not buttonClicked 


buttonClicked  = False # Bfore first click

b = Button(master, text="Smth", command=callback)
b.pack()

mainloop()

The code, changes the variable value from False to True (or reverse) every time you press the button.

Here's a runnable answer. In addition to changing the commmand= keyword argument so it doesn't call the function when the tk.Buttons are created, I also removed the event argument from the corresponding function definitions since tkinter doesn't pass any arguments to widget command functions (and your function don't need it, anyway).

You seem to be confusing event handlers with widget command function handlers. The former do have an event argument passed to them when they're called, but the latter typically don't (unless you do additional stuff to make it happen—it's a fairly common thing to need/want to do and is sometimes referred to as theThe extra arguments trick).

import tkinter as tk

# added only to define required global variable "txt"
class Txt(object):
    def SetValue(data): pass
    def GetValue(): pass
txt = Txt()
####

def load():
    with open(textField.get()) as file:
        txt.SetValue(file.read())

def save():
    with open(textField.get(), 'w') as file:
        file.write(txt.GetValue())

win = tk.Tk()
win.title('Text Editor')
win.geometry('500x500')

# create text field
textField = tk.Entry(win, width=50)
textField.pack(fill=tk.NONE, side=tk.TOP)

# create button to open file
openBtn = tk.Button(win, text='Open', command=load)
openBtn.pack(expand=tk.FALSE, fill=tk.X, side=tk.TOP)

# create button to save file
saveBtn = tk.Button(win, text='Save', command=save)
saveBtn.pack(expand=tk.FALSE, fill=tk.X, side=tk.TOP)

win.mainloop()

So you can set the relief of the button using its config, this makes it look like it is pressed.

def save(self):
    self.button0.config(relief=SUNKEN)
    # if you also want to disable it do:
    # self.button0.config(state=tk.DISABLED)
    #...

def stop(self):
    self.button0.config(relief=RAISED)
    # if it was disabled above, then here do:
    # self.button0.config(state=tk.ACTIVE)
    #...

EDIT

This doesn't work on Mac OSx apparently. This link shows how in should look: http://www.tutorialspoint.com/python/tk_relief.htm

Set a flag when the button is pressed, unset the flag when the button is released. There's no need for a loop since you're already running a loop (mainloop)

from Tkinter import * 
running = False
root = Tk()
def start_motor(event):
    global running
    running = True
    print("starting motor...")

def stop_motor(event):
    global running
    print("stopping motor...")
    running = False

button = Button(root, text ="forward")
button.pack(side=LEFT)
button.bind('<ButtonPress-1>',start_motor)
button.bind('<ButtonRelease-1>',stop_motor)
root.mainloop()

Assuming that you actually want to do something while the key is pressed, you can set up an animation loop using after. For example, to call a print statement once a second while the button is pressed you can add a function that does the print statement and then arranges for itself to be called one second later. The stop button merely needs to cancel any pending job.

Here's an example. The main difference to the original code is the addition of a move function. I also added a second button to show how the same function can be used to go forward or backward.

from Tkinter import * 
running = False
root = Tk()
jobid = None

def start_motor(direction):
    print("starting motor...(%s)" % direction)
    move(direction)

def stop_motor():
    global jobid
    root.after_cancel(jobid)
    print("stopping motor...")

def move(direction):
    global jobid
    print("Moving (%s)" % direction)
    jobid = root.after(1000, move, direction)

for direction in ("forward", "backward"):
    button = Button(root, text=direction)
    button.pack(side=LEFT)
    button.bind('<ButtonPress-1>', lambda event, direction=direction: start_motor(direction))
    button.bind('<ButtonRelease-1>', lambda event: stop_motor())

root.mainloop()

You can create bindings for the <ButtonPress> and <ButtonRelease> events independently.

A good starting point for learning about events and bindings is here: http://effbot.org/tkinterbook/tkinter-events-and-bindings.htm

Here's a working example:

import Tkinter as tk
import time

class Example(tk.Frame):
    def __init__(self, *args, **kwargs):
        tk.Frame.__init__(self, *args, **kwargs)
        self.button = tk.Button(self, text="Press me!")
        self.text = tk.Text(self, width=40, height=6)
        self.vsb = tk.Scrollbar(self, command=self.text.yview)
        self.text.configure(yscrollcommand=self.vsb.set)

        self.button.pack(side="top")
        self.vsb.pack(side="right", fill="y")
        self.text.pack(side="bottom", fill="x")

        self.button.bind("<ButtonPress>", self.on_press)
        self.button.bind("<ButtonRelease>", self.on_release)

    def on_press(self, event):
        self.log("button was pressed")

    def on_release(self, event):
        self.log("button was released")

    def log(self, message):
        now = time.strftime("%I:%M:%S", time.localtime())
        self.text.insert("end", now + " " + message.strip() + "\n")
        self.text.see("end")

if __name__ == "__main__":
    root = tk.Tk()
    Example(root).pack(side="top", fill="both", expand=True)
    root.mainloop()

You already had your event function. Just correct your code to:

   """Create Submit Button"""
    self.submitButton = Button(master, command=self.buttonClick, text="Submit")
    self.submitButton.grid()

def buttonClick(self):
    """ handle button click event and output text from entry area"""
    print('hello')    # do here whatever you want

This is the same as in @Freak's answer except for the buttonClick() method is now outside the class __init__ method. The advantage is that in this way you can call the action programmatically. This is the conventional way in OOP-coded GUI's.