Blocking The Tab Key - python

I've recently made a text editor with tkinter for python.
I need a way to disable tab from being able to be used normally, so it doesn't indent.
Does anyone have any idea as to how I would achieve this?
Thank you for your time.

It really depends on exactly what you did. Without more information I'm going to assume that you have a text widget somewhere and that you want to disable tab from indenting there.
Example:
from tkinter import Tk, Text
def no_tab(event):
return 'break'
root = Tk()
text_widget = Text()
text_widget.pack()
text_widget.bind('<Tab>', no_tab)
root.mainloop()
In this example we bind the <Tab> key to the function no_tab. So everytime tab is pressed within the text widget the no_tab function is called. The no_tab function returns the magic string 'break' which means that the action of the key won't be preformed and thus disabling the indentation that the tab key would have created otherwise.

Related

How to remove blank line at end of tkinter textbox?

When I run this code, it adds a blank line to the bottom of my textbox. I want my textbox to just show NEW TEXT after return is pressed, and I cannot figure out how to accomplish it. I searched on this site and could not find an answer, so apologies in advance if this is a duplicate question.
import tkinter as tk
def update(event):
entry.delete('1.0', tk.END)
entry.insert('1.0', 'NEW TEXT')
if entry.get('end-1c', 'end') == '\n':
entry.delete('end-1c', 'end')
root = tk.Tk()
root.config(bg='snow3')
root.geometry('200x200')
entry = tk.Text(root, height=1.3, width=12)
entry.bind('<Return>', update)
entry.configure(wrap='none')
entry.pack()
root.mainloop()
You cannot remove the final newline. That is baked into the text widget.
However, the problem is not the built-in newline. The problem is that the return key is inserting a newline after your function runs. That is because your binding happens before the built-in bindings, which is an important part of the way tkinter handles key bindings (and is a brilliant design!).
In short, this is what happens:
user presses the return key
your function is called from a widget-specific binding
your function deletes everything
your function inserts new text
your function returns
the Text widget class binding inserts a newline
To prevent that last step from happening, you need to return the string "break" from your function. That will prevent the default behavior defined by the Text widget from happening. The end result is that the changes you made to the widget in your function are the only changes made to the widget when the user presses the return key.
def update(event):
entry.delete('1.0', tk.END)
entry.insert('1.0', 'NEW TEXT')
return "break"
For a slightly longer explanation of why this happens, see this answer to the question Basic query regarding bindtags in tkinter.

Readonly tkinter text widget

I want to use tkinter text widget as a readonly widget. It should act as a transcript area. My idea is to keep this transcript in a file and whenever the user writes anything, just remove all the contents of the widget, and rewrite it again.
The code will look like:
transcript_entry = SimpleEditor() # SimpleEditor is inherited from ScrolledText
transcript_entry.text.delete("1.0", END)
# this is just a test string, it should be the contents of the transcript file
transcript_entry.text.insert("1.0", "This is test transcript")
transcript_entry.text.bind("<KeyPress>", transcript_entry.readonly)
And readonly function will look like:
def readonly(self, event):
self.text.delete("1.0", END)
# this is just a test string, it should be the contents of the transcript file
self.text.insert("1.0", "This is test transcript")
The bug here is that the last character entered by the user is added to the transcript. I suspect the reason is that the readonly function is called, then the user input is wrote to the widget. How to reverse this order & let the readonly function be called after the user input is wrote to the widget?
Any hints?
The reason that the last character is inserted is because the default bindings (which causes the insert) happens after custom bindings you put on the widget. So your bindings fire first and then the default binding inserts the characters. There are other questions and answers here that discuss this in more depth. For example, see https://stackoverflow.com/a/11542200/
However, there is a better way to accomplish what you are trying to do. If you want to create a readonly text widget, you can set the state attribute to "disabled". This will prevent all inserts and deletes (and means you need to revert the state whenever you want to programmatically enter data).
On some platforms it will seem like you can't highlight and copy text, but that is only because the widget won't by default get focus on a mouse click. By adding a binding to set the focus, the user can highlight and copy text but they won't be able to cut or insert.
Here's an example using python 2.x; for 3.x you just have to change the imports:
import Tkinter as tk
from ScrolledText import ScrolledText
class Example(tk.Frame):
def __init__(self, parent):
tk.Frame.__init__(self, parent)
t = ScrolledText(self, wrap="word")
t.insert("end", "Hello\nworld")
t.configure(state="disabled")
t.pack(side="top", fill="both", expand=True)
# make sure the widget gets focus when clicked
# on, to enable highlighting and copying to the
# clipboard.
t.bind("<1>", lambda event: t.focus_set())
if __name__ == "__main__":
root = tk.Tk()
Example(root).pack(fill="both", expand=True)
root.mainloop()
Please do not delete and reinsert your text :
It is huge performance issue.
It will remove any tags and marks set on the text
This will be visible to the user, and users don't like flickering interfaces
This is not necessary, Tkinter is customizable enough to just not allow the user change the content.
The best way I found to create a read only Text is to disable all the bindings leading to a text change.
My solution is to create a new Widget binding map containing only "read only commands". Then, just reconfigure your widget to use the new RO binding map instead of the default one :
from Tkinter import *
# This is the list of all default command in the "Text" tag that modify the text
commandsToRemove = (
"<Control-Key-h>",
"<Meta-Key-Delete>",
"<Meta-Key-BackSpace>",
"<Meta-Key-d>",
"<Meta-Key-b>",
"<<Redo>>",
"<<Undo>>",
"<Control-Key-t>",
"<Control-Key-o>",
"<Control-Key-k>",
"<Control-Key-d>",
"<Key>",
"<Key-Insert>",
"<<PasteSelection>>",
"<<Clear>>",
"<<Paste>>",
"<<Cut>>",
"<Key-BackSpace>",
"<Key-Delete>",
"<Key-Return>",
"<Control-Key-i>",
"<Key-Tab>",
"<Shift-Key-Tab>"
)
class ROText(Text):
tagInit = False
def init_tag(self):
"""
Just go through all binding for the Text widget.
If the command is allowed, recopy it in the ROText binding table.
"""
for key in self.bind_class("Text"):
if key not in commandsToRemove:
command = self.bind_class("Text", key)
self.bind_class("ROText", key, command)
ROText.tagInit = True
def __init__(self, *args, **kwords):
Text.__init__(self, *args, **kwords)
if not ROText.tagInit:
self.init_tag()
# Create a new binding table list, replace the default Text binding table by the ROText one
bindTags = tuple(tag if tag!="Text" else "ROText" for tag in self.bindtags())
self.bindtags(bindTags)
text = ROText()
text.insert("1.0", """A long text with several
lines
in it""")
text.pack()
text.mainloop()
Note that just the bindings are changed. All the Text command (as insert, delete, ...) are still usable.
I recently worked a different, slightly simpler solution. Rather than changing all the bindings, one can add a function to delete all input characters as soon as they are written:
def read_only(self, event):
if event.char is not '': # delete only if the key pressed
# corresponds to an actual character
self.text.delete('insert-1c')
and just bind it to any event:
root.bind('<Key>', self.read_only)

Tkinter, Entry widget, is detecting input text possible?

I have an Entry widget on a simple calculator. The user can choose to enter an equation via the keypad. I was wondering if there was a way to detect a character(from the keypad in my case) being typed into the Entry widget. So, focus is on the widget, user presses '4', it comes up on the widget... can I detect this act, for basic purposes of logging the input?
Every time you press a key inside a Tkinter window, a Tkinter.Event instance is created. All you need to do is access that instance. Here is a simple script that demonstrates just how:
from Tkinter import Tk, Entry
root = Tk()
def click(key):
# print the key that was pressed
print key.char
entry = Entry()
entry.grid()
# Bind entry to any keypress
entry.bind("<Key>", click)
root.mainloop()
key (being a Tkinter.Event instance) contains many different attributes that can be used to get almost any type of data you want on the key that was pressed. I chose to use the .char attribute here, which will have the script print what each keypress is.
Yes. There are a few different ways to do this, in fact.
You can create a StringVar, attach it to the Entry, and trace it for changes; you can bind all of the relevant events; or you can add a validation command that fires at any of several different points in the sequence. They all do slightly different things.
When a user types 4, there's a key event with just the 4 in it (which doesn't let you distinguish whether the user was adding 4 to the end, or in the middle, or replacing a whole selected word, or…), and then a modification event is fired with the old text,* and then the "key" or "all" validation function is called with the (proposed) new text, and the variable is updated with the (accepted) new text (unless the validation function returned false, in which case the invalidcommand is called instead).
I don't know which one of those you want, so let's show all of them, and you can play around with them and pick the one you want.
import Tkinter as tk
root = tk.Tk()
def validate(newtext):
print('validate: {}'.format(newtext))
return True
vcmd = root.register(validate)
def key(event):
print('key: {}'.format(event.char))
def var(*args):
print('var: {} (args {})'.format(svar.get(), args))
svar = tk.StringVar()
svar.trace('w', var)
entry = tk.Entry(root,
textvariable=svar,
validate="key", validatecommand=(vcmd, '%P'))
entry.bind('<Key>', key)
entry.pack()
root.mainloop()
The syntax for variable trace callbacks is a bit complicated, and not that well documented in Tkinter; if you want to know what the first two arguments mean, you need to read the Tcl/Tk docs, and understand how Tkinter maps your particular StringVar to the Tcl name 'PY_VAR0'… Really, it's a lot easier to just build a separate function for each variable and mode you want to trace, and ignore the args.
The syntax for validation functions is even more complicated, and a lot more flexible than I've shown. For example, you can get the inserted text (which can be more than one character, in case of a paste operation), its position, and all kinds of other things… but none of this is described anywhere in the Tkinter docs, so you will need to go the Tcl/Tk docs. The most common thing you want is the proposed new text as the argument, and for that, use (vcmd, '%P').
Anyway, you should definitely play with doing a variety of different things and see what each mechanism gives you. Move the cursor around or select part of the string before typing, paste with the keyboard and with the mouse, drag and drop the selection, hit a variety of special keys, etc.
* I'm going to ignore this step, because it's different in different versions of Tk, and not very useful anyway. In cases where you really need a modified event, it's probably better to use a Text widget and bind <<Modified>>.
If you just need to do simple things without using trace module you can try
def objchangetext(self, textwidget):
print(textwidget.get()) #print text out to terminal
text1 = tk.Entry(tk.Tk())
text1.bind("<KeyRelease>", lambda event, arg=(0): objchangetext(text1))

Function when entered in text box?

I'm using Tkinter for a small Python application. It has a set of ratio buttons, a text box, and a button. Is there a way to make it so the user can simply press Enter/Return on a keyboard and run the same function the button runs? The text box stays selected even when a radio is changed, so that won't cause any problems.
You should be able to bind an event handler to either the text box widget or the whole application that will be called when the event happens. Assuming you have a function to handle the event, something along the lines of:
widget.bind('<Return>', event_handler)
You can also bind a handler function at the application level by calling the bind_all() method of any widget, e.g.:
self.bind_all('<Return>', self.event_handler)
Note the key name is Return not Enter. See Key Names for a list of them all. You can also prefix the key name with a modifier like Shift- and Control- if desired.
There's a decent online reference for tkinter 8.4 here.

How do you modify the current selection length in a Tkinter Text widget?

I would like to be able to double click on test,
in a Tkinter Text widget, and have it select test (and exclude the comma).
Here is what I've tried:
import Tkinter as tk
def selection_mod(event=None):
result = aText.selection_get().find(',')
if result > 0:
try:
aText.tag_add("sel", "sel.first", "sel.last-1c")
except tk.TclError:
pass
lord = tk.Tk()
aText = tk.Text(lord, font=("Georgia", "12"))
aText.grid()
aText.bind("<Double-Button-1>", selection_mod)
lord.mainloop()
The first issue is that <Double-Button-1> seems to trigger the handler before the selection is made, producing:
TclError: PRIMARY selection doesn't exist or form "STRING" not defined
The second issue is that even when using a binding that works,
my selection tag doesn't seem to do anything.
It doesn't even raise an error, and I've tried without the except tk.TclError:.
Your binding is happening before the default bindings occur. Thus, the selection doesn't yet exist when your binding fires. Because your binding tries to get the selection, it fails with the error that you see.
You will need to arrange for your binding to happen after the class bindings. A cheap hack is to use after to execute your code once the default bindings have a chance to work. Or, you can use the bindtag feature to make sure your binding fires after the default bindings.
The second problem is that you don't clear the old selection before setting the new. You'll want to do tag_remove to first remove the existing selection. Otherwise, the comma (if it was somehow selected) will remain selected since all you're doing is re-applying the tag to text that already has the tag.
However, double-click doesn't normally capture the comma so I don't quite understand then point of your code. At least, when I test it on OSX it doesn't include the comma.
Here is what I came up with thanks to Bryan's answer:
import Tkinter as tki # tkinter in Python 3
def selection_mod(event=None):
result = txt.selection_get().find(',')
if result > 0:
fir, sec = txt.tag_ranges("sel")
txt.tag_remove("sel", "sel.first", "sel.last")
txt.tag_add("sel", fir, str(sec)+"-1c")
root = tki.Tk()
txt = tki.Text(root, font=("Georgia", "12"))
txt.grid()
txt.bind("<Double-Button-1>", lambda x: root.after(20, selection_mod))
root.mainloop()
It's worth noting that I'm using Windows 7, and according to Bryan,
OSX doesn't include the comma when you double click a word.

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