Validation for Tkinter Entry Runs Only Once

I am trying to implement a way of an entry only accepting integers being typed into it but I am struggling to get the code to work as desired. As I understand:

The entry widget has a parameter validate which chooses when the validation should take place.
The parameter validatecommand decides how the data should be restricted
When validate is equal to 'key', at every keystroke, the string inside the entry is checked against the rules specified in validatecommand

However, after attempting this I got the issue that it only the validates the string in the entry at the before even clicking on it.

from tkinter import*
root = Tk()

def equationpage(root):
    vcmd = root.register(validate)
    A_str = IntVar()
    A_str.set(1)
    a = Entry(root,width="2",textvariable=A_str,validate = "key",validatecommand = (vcmd,'%p'))
    a.place(x=0,y=0)
def validate(inp):
    try:
        float(inp)
    except:
        return False
    return True
equationpage(root)
mainloop()

With the code above no validation takes place and it lets me type anything into the entry. If I change the code above so that there is no default value for the entry I end up not being able to type anything into the entry as it keeps rejecting the input.

How can I solve this problem?

Solution

Based on this answer, there's no defined Tcl variable: '%p' for this option.

Replace:

'%p'

to include the uppercase P instead:

'%P'