Tkinter event handlers and command callbacks

[luofeiyu]

from Tkinter import *
fields = 'Name', 'Job', 'Pay'
 
def fetch(event,entries):
   for entry in entries:
       print 'Input => "%s"' % entry.get()       # get text
       print  event.widget 
 
 
def makeform(root, fields):
   entries = []
   for field in fields:
       row = Frame(root)                           # make a new row
       lab = Label(row, width=5, text=field)       # add label, entry
       ent = Entry(row)
       row.pack(side=TOP, fill=X)                  # pack row on top
       lab.pack(side=LEFT)
       ent.pack(side=RIGHT, expand=YES, fill=X)    # grow horizontal
       entries.append(ent)
   return entries
 
if __name__ == '__main__':
   root = Tk()
   ents = makeform(root, fields)
   root.bind('<Return>', lambda event,entries=ents: fetch(event,entries))       
   Button(root, text='Fetch', command= lambda event:fetch(event,entries)).pack(side=LEFT)  # #how to revise it?
   root.mainloop()
 

in the code ,the bind method is ok, how to revise "command=lambda event:fetch(event,entries)",to make it work too??

[bvdet]

The button command callback does not receive an argument. If you want the button to respond to an event and the callback receive the event as an argument, bind an event to it, possibly "<ButtonRelease-1>".

from Tkinter import *
fields = 'Name', 'Job', 'Pay'
 
def fetch(entries, event=None):
   for entry in entries:
       print 'Input => "%s"' % entry.get()       # get text
       if event:
           print  event.widget 
 
 
def makeform(root, fields):
   entries = []
   for field in fields:
       row = Frame(root)                           # make a new row
       lab = Label(row, width=5, text=field)       # add label, entry
       ent = Entry(row)
       row.pack(side=TOP, fill=X)                  # pack row on top
       lab.pack(side=LEFT)
       ent.pack(side=RIGHT, expand=YES, fill=X)    # grow horizontal
       entries.append(ent)
   return entries
 
if __name__ == '__main__':
   root = Tk()
   ents = makeform(root, fields)
   root.bind('<Return>', lambda event, entries=ents: fetch(entries, event))
   Button(root, text='Fetch', command=lambda:fetch(ents)).pack(side=LEFT)  # #how to revise it?
   root.mainloop()

[dwblas]

First, your title makes this thread appear to be a "HowTo", i.e. code that explains how to do something, so you may get fewer readers/respondents as a result.

how to revise "command=lambda event:fetch(event,entries)",to make it work too??

What does this mean? If you mean that your want to pass something to a function when a button is pressed, Python provides "partial". Note that Guido does not like lambda, and planned to remove it in Python 3 as there are better ways to do things. Also, in the fetch() function, you print the same event for each entry in entries. It should be indented at the same level as the for() statement so it only prints once.

from Tkinter import *
from functools import partial
 
def fetch(event, entries):
       for entry in entries:
           print 'Input => "%s"' % entry.get()       # get text
           if event:
               print  event.widget 
 
 
def makeform(root, fields):
       entries = []
       for field in fields:
           row = Frame(root)                           # make a new row
           lab = Label(row, width=5, text=field)       # add label, entry
           ent = Entry(row)
           row.pack(side=TOP, fill=X)                  # pack row on top
           lab.pack(side=LEFT)
           ent.pack(side=RIGHT, expand=YES, fill=X)    # grow horizontal
           entries.append(ent)
       return entries
 
if __name__ == '__main__':
       fields = 'Name', 'Job', 'Pay'
       root = Tk()
       ents = makeform(root, fields)
 
       ## this can be converted to "partial" as well if you want
       root.bind('<Return>', lambda event, entries=ents: fetch(entries, event))
 
       xb =Button(root, text='Fetch')
       xb.pack(side=LEFT)
 
       ## note that both 'root' & 'xb' bind an object to an event
       ## that is sent to the function
       xb.bind("<Button-1>", partial(fetch, entries=ents))
       root.mainloop() 

[luofeiyu]

from Tkinter import *
 
def fetch(x):
       print  x.type,x
 
 
if __name__ == '__main__':
       root = Tk()
       root.bind('<Return>', fetch)
       root.mainloop()
 

i can get output :
2 <Tkinter.Event instance at 0xb742986c>

from Tkinter import *
 
def fetch(x):
       print  x.type,x
 
 
if __name__ == '__main__':
       root = Tk()
       button=Button(root,text='Fetch')
       button.pack()
       button.bind('<Return>',fetch)       
       root.mainloop()
 

why i can get nothing when i click enter??

[dwblas]

To capture a "Return", you have to set the focus. Otherwise, the focus is not set on the widget so the Return goes to the root window or whatever has focus, and you don't have any bindings for it.

rom Tkinter import *
 
def fetch(x):
       print x, type(x)
 
if __name__ == '__main__':
       root = Tk()
       button=Button(root,text='Fetch')
       button.pack()
       button.focus_set()
       button.bind('<Return>',fetch)       
       root.mainloop() 

[luofeiyu]

you lose f in rom (it is from),i made a try,it'ok,but there is still a problem,
when i finish my first enter,it's ok,there is output ,
when i have a try for the second time ,there is no output??

[bvdet]

Are you losing focus after the first event? You can reset the focus in the callback with x.widget.focus_set()

[luofeiyu]

from Tkinter import *
 
def fetch(x):
           print x, type(x)
 
if __name__ == '__main__':
           root = Tk()
           button=Button(root,text='Fetch')
           button.pack()
           button.focus_set()
           button.grab_set()
           button.bind('<Return>',fetch)       
           root.mainloop() 

add button.grab_set(),it's ok now