New submission from alan hoover <alan.hoo...@gmail.com>:
Background:
building a screen using Tkinter based on information from a database to let
user take action on the database rows. I don't know how many rows there will
be, so I'm storing the widgets in arrays for each column.
Code:
for row in getDBrows():
self.buttons.append(Tkinter.Button(self,text='UnLoad it', command=lambda
:self.unload(row[0])))
Problem:
When executing the above code, all the buttons have the key to the database
table that belongs to the last row. I found a work around -- by moving the
call to create the button (containing the lambda) to a separate function and
call that function to create the button instead of creating the button
directly, the buttons then make their callback with a correct database key.
Workaround:
for row in getDBrows():
self.buttons.append(self.buildbutton(row[0]))
.
.
def buildbutton(self,key):
return Tkinter.Button(self,text='UnLoad it', command=lambda:
self.unload(key))
When using the workaround code instead of the original code, the button
for each row has the appropriate key to the database.
Speculation:
It acts like the lambda definitions don't get solidified until the containing
block exits; at that time, the lambda definition(s) get locked in with the
current value of the variable getting passed into the lambda as a parameter.
By moving the lambda call to a different block (separate function), the lambda
gets "locked" when that block (function) exits instead of when the containing
block (loop) exits.
----------
components: IDLE, Tkinter, Windows
messages: 102120
nosy: alan.hoover
severity: normal
status: open
title: series of lamdas in loop sets the paramater on all calls to that of the
last call
type: behavior
versions: Python 2.6
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Python tracker <rep...@bugs.python.org>
<http://bugs.python.org/issue8283>
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