save as file dialog - how to not allow overwrite

Question

I'm trying to make a savefile dialog in tkinter. I need to save the file name to use later. However, I do not want the filedialog to accept selecting an already existing file name.

So far I only have this:

from tkinter import filedialog

my_file = filedialog.asksaveasfilename(defaultextension = ".myfile", 
                                       filetypes = [("MY SUPER FILE", ".myfile"), 
                                                    ("All files", ".*")])

One possibility would be to get the file name, check if it exists (using os.path.isfile) and ask again the user for new name if there is already a file with the same name. However, the tkinter filedialog asks the user "file already exists. do you want to overwrite?". So it seems confusing if later I tell the user that I do not accept the filename choice. Is there a way to force the tkinter filedialog to not ask the user about the overwriting?

Edit: Based on the suggestions in the answers, I tried to make my own save file dialog.

I basically only added a warning to the tkinter save dialog:

class MySaveFileDialog(filedialog.FileDialog):

""" File save dialog that does not allow overwriting of existing file"""
def ok_command(self):
    file = self.get_selection()
    if os.path.exists(file):
        if os.path.isdir(file):
            self.master.bell()
            return
        messagebox.showarning("The current file name already exists. Please give another name to save your file.")
    else:
        head, tail = os.path.split(file)
        if not os.path.isdir(head):
            self.master.bell()
            return
    self.quit(file)

So, it looks pretty simple. Then I thought: I need to create my own asksaveasfilename function. I went to check the source:

def asksaveasfilename(**options):
"Ask for a filename to save as"

return SaveAs(**options).show()

Humm.. I need to see what is SaveAs doing.

class SaveAs(_Dialog):
    "Ask for a filename to save as"

    command = "tk_getSaveFile"

Aaannddd... i'm lost. I don't understand how this pieces fit together. 'SaveAs' just has the command tk_getSaveFile. How is the SaveFileDialog being used here? And how can I make my own myasksaveasfilename function?

Answer 1

There is no such option. If you want to get rid of the security question, then you'll have to write your own file dialog.

If you look at filedialog.py, you'll see that the dialog is implemented in Python. So all you have to do is to extend the class SaveFileDialog and override the method ok_command() with one that doesn't allow to select an existing file name.

You can use most of the existing code and just change a few texts to achieve your goal.

I haven't tested it but this code should work:

def ok_command(self):
        file = self.get_selection()
        if os.path.exists(file):
            if os.path.isdir(file):
                self.master.bell()
                return
            d = Dialog(self.top,
                       title="Overwrite Existing File",
                       text="You can't overwrite an existing file %r. Please select a new name." % (file,),
                       bitmap='error',
                       default=0,
                       strings=("OK",))
            return
        else:
            head, tail = os.path.split(file)
            if not os.path.isdir(head):
                self.master.bell()
                return
        self.quit(file)