MaskedInput ValueError Value does not match template

[JonathanPlasse]

Have you checked closed issues? https://github.com/Textualize/textual/issues?q=is%3Aissue+is%3Aclosed

Yes, no issue mentioned problems with MaskedInput validation.

Have you checked against the most recent version of Textual? https://pypi.org/search/?q=textual

Yes

Please give a brief but clear explanation of the issue. If you can, include a complete working example that demonstrates the bug. Check it can run without modifications.

1. Run the app

uv run --script masked_input_value_error.py

2. Press the key e or any other non digit.
3. Watch the app crash with a ValueError.

masked_input_value_error.py

# /// script
# requires-python = ">=3.13"
# dependencies = [
#     "textual==1.0.0",
# ]
# ///
from textual.app import App, ComposeResult
from textual.widgets import MaskedInput


class BugApp(App[None]):
    def compose(self) -> ComposeResult:
        yield MaskedInput("9", "9")


app = BugApp()
app.run()

It will be helpful if you run the following command and paste the results:

textual diagnose

If you don't have the textual command on your path, you may have forgotten to install the textual-dev package.

Feel free to add screenshots and / or videos. These can be very helpful!

Screencast.from.2025-01-24.22-33-57.mp4

Textual Diagnostics

Versions

Name	Value
Textual	1.0.0
Rich	13.9.4

Python

Name	Value
Version	3.13.0
Implementation	CPython
Compiler	Clang 18.1.8
Executable	/home/jonathan/.cache/uv/archive-v0/uhCuU97F8DMiIyfN6OiqV/bin/python

Operating System

Name	Value
System	Linux
Release	6.12.9-100.fc40.x86_64
Version	#1 SMP PREEMPT_DYNAMIC Thu Jan 9 16:04:00 UTC 2025

Terminal

Name	Value
Terminal Application	vscode (1.96.4)
TERM	xterm-256color
COLORTERM	truecolor
FORCE_COLOR	Not set
NO_COLOR	Not set

Rich Console options

Name	Value
size	width=142, height=23
legacy_windows	False
min_width	1
max_width	142
is_terminal	True
encoding	utf-8
max_height	23
justify	None
overflow	None
no_wrap	False
highlight	None
markup	None
height	None

[github-actions]

We found the following entries in the FAQ which you may find helpful:

• Why doesn't Textual look good on macOS?
• No widget called TextLog

Feel free to close this issue if you found an answer in the FAQ. Otherwise, please give us a little time to review.

This is an automated reply, generated by FAQtory

[JonathanPlasse]

After some investigation, it seems that the problem comes from MaskedInput not implementing replace to filter out bad characters.
How should MaskedInput behave when the text is selected but the inputted value is invalid?

• Should the inputted value be ignored and keep the old value?
• Should the inputted value be modified to use spaces instead of invalid characters?

[TomJGooding]

Good catch. I think this also shows another problem with the MaskedInput which I've raised as a separate issue:

• MaskedInput does not highlight the selected text #5495