Member Avatar for Archenemie

I've tried every way I can possibly see to try and convert the value from the numctrl to a decimal but the problem lies with the retrieved value being a float.

I cant covert the float to a string first because it looses the trailing 0 in values such as 1.30 which I need because I am trying to represent currency.

Does anyone know the way forward or what I am doing wrong please?

import wx
from wx.lib.masked import NumCtrl
from decimal import *

class MyFrame(wx.Frame):

    def __init__(self, parent, id):
        wx.Frame.__init__(self, parent, id, 'Quick Silver', size = (180, 100))

        context = Context(prec = 2)
        setcontext(context)
        
        panel = wx.Panel(self)
        lolinput = wx.lib.masked.NumCtrl(panel, pos = (20,20), fractionWidth = 2) # for 2 decimal places.
        lolinput.SetValue(1.30)

        x = Decimal(lolinput.GetValue(), 2)
        context.create_decimal(x)
        print x

app = wx.App(redirect = False)
frame = MyFrame(parent = None, id = -1)
frame.Show()
app.MainLoop()
  • 4 Contributors
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  • Latest Post Latest Post by zentraders

Dani AI

Generated

Root cause and short answer: NumCtrl hands you a Python float when fractionWidth>0, and converting that float directly to a Decimal will carry binary‑float artifacts. Prefer constructing Decimal from the control’s textual value (so trailing zeros like "1.30" survive) or, if you really must start from a float, use the Decimal context conversion helpers. was right to flag the float->Decimal issue. (NumCtrl docs; Python decimal notes.) (docs.wxpython.org)

A robust workflow that avoids the epsilon hacks you tried () and the fragile float-format trick () is:

  • Keep fractionWidth=2 so the widget displays two decimals.
  • Grab the control’s plain text (no grouping/format characters) and turn that string straight into Decimal.
  • Use Decimal.quantize (or your Context) to force the exact scale and the rounding mode you want.

Example (illustrates the idea — uses methods that NumCtrl / MaskedEdit provide):

raw = numctrl.GetPlainValue()        # control text, preserves trailing zeros
raw = raw.replace(numctrl.GetDecimalChar(), '.')  # normalize locale decimal char
d = Decimal(raw)
d = d.quantize(Decimal('0.01'), rounding=ROUND_HALF_EVEN)

GetPlainValue() (and related masked control helpers) is described in the masked edit docs; NumCtrl API notes that GetValue() returns a float when a fractional width is set. (docs.wxpython.org)

If you already have a float and cannot get a string from the control, the decimal module exposes context helpers (e.g. create_decimal_from_float) that convert a float using your current context rather than importing the full binary expansion. This is more predictable than adding/subtracting tiny epsilons. For details and caveats see the Python decimal documentation. (docs.python.org)

Troubleshooting checklist: confirm fractionWidth is set, inspect GetPlainValue() output for the exact characters (watch locale decimal separators), choose an explicit rounding mode for quantize, and avoid constructing Decimal from raw floats.

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All 6 Replies

Member Avatar for Archenemie

Tried quantize to no avail

import wx
from wx.lib.masked import NumCtrl
from decimal import *

class MyFrame(wx.Frame):

    def __init__(self, parent, id):
        wx.Frame.__init__(self, parent, id, 'Quick Silver', size = (180, 100))
        
        panel = wx.Panel(self)
        lolinput = wx.lib.masked.NumCtrl(panel, pos = (20,20), fractionWidth = 2) # for 2 decimal places.
        lolinput.SetValue(1.30)

        x = Decimal(lolinput.GetValue())
        Decimal(x).quantize(Decimal('.01'), rounding=ROUND_DOWN)

        print x

app = wx.App(redirect = False)
frame = MyFrame(parent = None, id = -1)
frame.Show()
app.MainLoop()
Member Avatar for woooee

try and convert the value from the numctrl to a decimal

You can not convert a float to decimal.Decimal because floats are inaccurate past a certain number of digits. You will have to get/enter the value as a string and convert.

Member Avatar for Archenemie

Solved it by fiddling around with data types

import wx
from wx.lib.masked import NumCtrl
from decimal import *

class MyFrame(wx.Frame):

    def __init__(self, parent, id):
        wx.Frame.__init__(self, parent, id, 'Quick Silver', size = (180, 100))

        getcontext().prec = 3
        
        panel = wx.Panel(self)
        lolinput = wx.lib.masked.NumCtrl(panel, pos = (20,20), fractionWidth = 2) # for 2 decimal places.
        lolinput.SetValue(1.30)

        x = lolinput.GetValue()
        x = x + 0.001
        x = Decimal(x) - Decimal("0.001")
        Decimal(x).quantize(Decimal('.01'), rounding=ROUND_DOWN)

        print x

app = wx.App(redirect = False)
frame = MyFrame(parent = None, id = -1)
frame.Show()
app.MainLoop()
Member Avatar for Gribouillis

Why not x = Decimal('{0:.2f}'.format(lolinput.GetValue()), 2) ?

Member Avatar for Archenemie

Yours would more than likely have worked fine grib and I may actually use it tbh.

They way I solved it in the end was create a function call.

self.Round2DP(lolinput)

    def Round2DP(self, event):

        x = event.GetValue()
        x = x + 0.001
        x = Decimal(x) - Decimal("0.001")
        Decimal(x).quantize(Decimal('.01'), rounding=ROUND_DOWN)

        print x
        return x
Edited by Archenemie because: n/a
Member Avatar for zentraders

Why not just do something like
x = 12.30
x_str = "%5.2f" % (x+0.004)

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