check entry inputs in tkinter using a function - python-2.7

Question

I trying to create physics calculator using python tkinter but I find it quite difficult. I have done this calculator in Command line interface but I a bit different with tkinter. basically, I have 5 entry boxes and above each one of them a button. the user will insert values in three of them and should press the button on top of each unknown value to make the calculation and get the result. my main issue is how can I create a function that evaluates the inputs in my entry boxes and make the calculation then print the results inside the entry box. I made some coding but unfortunately the operation is not working due to few mistakes.
here is my coding part:
from Tkinter import *
import math
class calculator():
def is_positive_number(number): # validation function
if number <= 0:
return False
else :
return True
def value_of_time(prompt):
while True: # loop command for time
try:
valid = False
while not valid:
value = float((prompt))
if is_positive_number(value):
valid = True
return value
else :
valid = False
print ('I donot know what is happening')
except ValueError:
print("Oops, unfortunately this is a wrong input, please try again.")
#better try again... Return to the start of the loop
continue
else:
#value was successfully parsed!
#we're ready to exit the loop.
break
def input_of_box(prompt):
while True: # loop for initial velocity
try:
value = float(input(prompt))
return value
except ValueError:
print("Oops, we are you not typing a number, please try again.")
#better try again... Return to the start of the loop
continue
else:
#value was successfully parsed!
#we're ready to exit the loop.
break
# def minput(numberofinput):
if numberofinput == 1:
t = value_of_time("Enter the time that takes an object to accelerate in seconds:")
return
elif numberofinput == 2:
u = input_of_box("Enter the initial velocity in m/s:")
return
elif numberofinput == 2:
v = input_of_box("Enter the final velocity in m/s:")
return
def my_calculation(mvariables): # this function is to operate the calculation
if mvariables == 1:
a = (v-u) /(t)
mentery1 = a
return
elif mvariables == 2:
v = u + a*t
mentery2 = v
return
elif mvariables == 3:
u = a*t - v
mentery3 = t
elif mvariables == 4:
t = (v - u)/a
mentery3 = t
return
elif mvariables == 5:
s = (v**2-u**2)/2*a
mentery4 = s
else:
print ('there is an error')
cal = Tk()
cal.configure(background='sky blue')
a = StringVar()
u = StringVar()
v = StringVar()
t = StringVar()
s = StringVar()
cal.geometry('650x420+350+225')
cal.title('Main Menu')
# here we start greating buttons and entry boxes
m_label = Label(text='Calculator',fg = 'Navy', font=("Helvetica", 20,"bold italic"), bg='sky blue')
m_label.pack()
button1 = Button(cal,text='A',fg='white',bg='dark green',bd =3, width=4, command= lambda : my_calculation(1))
button1.place(x=92,y=210)
mentery1 = Entry(cal, textvariable = a ,width=10,bd =3)
mentery1.place(x=82,y=240)
button2 = Button(cal,text='U',fg='white',bg='dark green',bd =3, width=4, command= lambda : my_calculation(3))
button2.place(x=192,y=210)
mentery2 = Entry(cal, textvariable = u ,width=10,bd =3)
mentery2.place(x=182,y=240)
button3 = Button(cal,text='V',fg='white',bg='dark green',bd =3, width=4, command= lambda : my_calculation(2))
button3.place(x=292,y=210)
mentery3 = Entry(cal, textvariable = v ,width=10,bd =3)
mentery3.place(x=282,y=240)
button4 = Button(cal,text='T',fg='white',bg='dark green',bd =3, width=4,command= lambda : my_calculation(4))
button4.place(x=392,y=210)
mentery4 = Entry(cal, textvariable = t ,width=10,bd =3)
mentery4.place(x=382,y=240)
button5 = Button(cal,text='S',fg='white',bg='dark green',bd =3, width=4,command= lambda : my_calculation(5))
button5.place(x=492,y=210)
mentery5 = Entry(cal, textvariable = s , width=10,bd =3)
mentery5.place(x=482,y=240)
# end of button commands
app = calculator()
app.mainloop()

Answer 1

For validating the input, do the following:
def returnValidatedInput(entry):
value = entry.get() # Get the text in the 'entry' widget
evaluation = eval(value) # Evaluate 'value'
return evaluation
And for inserting the answers into the entries (it's not called printing the answers into the entries):
def insertAnswer(entry, answer):
entry.delete(0, 'end') # Be sure the entry is empty, if it is not, clear it
entry.insert(END, str(answer)) # Insert the answer into the 'entry' widget.