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Recipe 11.3. Using Default Values and Bounds with tkSimpleDialog Functions
Credit: Mike Foord, Peter Cogolo
Problem
You need to get an input value from
the user with one of Tkinter's
tkSimpleDialog dialog functions, but you want to
add a default value, or to ensure that the value entered lies within
certain bounds.
Solution
Each of Tkinter's tkSimpleDialog
functions (askstring, askfloat,
askinteger) supports an optional default value, as
well as optional validation against minimum and maximum value.
However, this set of features is not clearly spelled out in the
documentation. Here's a wrapper function that you
may find preferable:
import tkSimpleDialog
_dispatch = { str: tkSimpleDialog.askstring,
int: tkSimpleDialog.askinteger,
float: tkSimpleDialog.askfloat,
}
def getinput(title, prompt, type=str, default=None, min=None, max=None):
''' gets from the user an input of type `type' (str, int or float),
optionally with a default value, and optionally constrained to
lie between the values `min' and `max' (included).
'''
f = _dispatch.get(type)
if not f:
raise TypeError, "Can't ask for %r input" % (type,)
return f(title, prompt, initialvalue=default,
minvalue=min, maxvalue=max)
Discussion
The built-in tkSimpleDialog module offers a few
simple functions that pop up dialogs that ask the user to input a
string, a float, or an integernot a very advanced user
interface but dirt-simple to use in your programs. Unfortunately,
while these functions do support a few nice extras (the ability to
pass in a default value, and having the result validated within
certain optional minimum and maximum values), the
module's documentation (what little there is of it)
does not make this feature clear. Even the
pydoc-generated page http://epydoc.sourceforge.net/stdlib/public/tkSimpleDialog-modulel
just says "see SimpleDialog class."
Since no such class exists, seeing it is not easy. (The relevant
class is actually named _QueryDialog, and due to
the leading underscore in the name, it is considered
"private". Therefore
pydoc does not build a documentation web page for
it.)This recipe shows how to access this functionality
that's already part of the Python Standard Library.
As a side benefit, it refactors the functionality into a single
getinput function that takes as an argument the type
of input desired (defaulting to str, meaning that
the default type of result is a string, just as for built-in function
raw_input). If you prefer the original concept of
having three separate functions, it's easy to modify
the recipe according to your tastes. The recipe mostly makes the
semi-hidden functionality of the original functions'
undocumented keyword arguments initialvalue,
minvalue and maxvalue manifest
and clearer through its optional parameters
default, min, and
max, which it passes right on to the underlying
original function.
See Also
tkSimpleDialog module documentation is at
http://epydoc.sourceforge.net/stdlib/public/tkSimpleDialog-modulel.
