Question

i am having trouble figuring out why my timer is not reaching zero when i run it. I am trying to get the window to close when a=0 but a keeping decreasing to negative digits why please? This is my codes

def close_timer(self):
    global a
    a = float(a - 0.1)
    self.labeltext.set(str(("%.1f" % (a))))
    a = float(a)
    print a
    print (a == 0)
    if a == 0:
        self.canvas.after(100)
        self.root.destroy()
    self.root.after(100,self.close_timer)

Answer 1

Floating point number math is generally inaccurate – you can’t represent a decimal 0.1 in binary floating points exactly, therefore you’ll never reach 0:

>>> a = 1
>>> while a > 0:
...     a = a - 0.1
...     print(repr(a))
...
0.9
0.8
0.7000000000000001
0.6000000000000001
0.5000000000000001
0.40000000000000013
0.30000000000000016
0.20000000000000015
0.10000000000000014
1.3877787807814457e-16
-0.09999999999999987

Use if abs(a) < 0.000001: or something similar.