Current Flow:-
- If you create a new file in idle and try to run it, the editor asks to save the file. However if user presses cancel button the code is not executed.

Problem:-
I have been using idle for over 5 years and this behavior is quite annoying(along with paste :) !!). We are often required to copy code from various sites say some tutorial or code samples which are good for one time usage.

Solution:-
If a user presses cancel button then set a flag in IOBinding say "optedTemp", save it to a named temporary file, execute the code and close the file. If user again runs the code, check for this flag. If it is true then there is no need to ask for saving the code and again create the temporary file, execute, close. If some one needs to save this code they can use the "save as" menu which sets off the optedTemp flag.

Here is the code I propose (check for "#+++++++++++++++++++++")

==================idlelib/ScriptBinding.py===============
# At top
import tempfile  #+++++++++++++++++++++

# New definition of functions:-


    def _run_module_event(self, event):
        filename = self.getfilename()
        tempCode = None #+++++++++++++++++++++
        if not filename:            
            tempCode = tempfile.NamedTemporaryFile(suffix = ".py") #+++++++++++++++++++++
            filename = tempCode.name #****Added***
            self.editwin.io.writefile( filename ) #+++++++++++++++++++++
            self.editwin.io.optedTemp = True #+++++++++++++++++++++
            #return 'break'
        code = self.checksyntax(filename)
        ......
        interp.runcode(code)
        if tempCode is not None: #+++++++++++++++++++++
            tempCode.close() #+++++++++++++++++++++
        return 'break'

    def getfilename(self):
        filename = self.editwin.io.filename
        if not self.editwin.get_saved():
            autosave = idleConf.GetOption('main', 'General',
                                          'autosave', type='bool')
            if autosave and filename:
                self.editwin.io.save(None)
            elif self.editwin.io.optedTemp: #+++++++++++++++++++++
                filename = None #+++++++++++++++++++++
            else:
                confirm = self.ask_save_dialog()
                self.editwin.text.focus_set()
                if confirm:
                    self.editwin.io.save(None)
                    filename = self.editwin.io.filename
                else:
                    filename = None
        return filename

============idlelib/IOBinding.py======================

def __init__(self, editwin):
        #....
        self.__id_print = self.text.bind("<<print-window>>", self.print_window)
        self.optedTemp = False #+++++++++++++++++++++

def save_as(self, event):
        filename = self.asksavefile()
        if filename:
            if self.writefile(filename):
                self.set_filename(filename)
                self.set_saved(1)
                self.optedTemp = False #+++++++++++++++++++++
                try:
                    self.editwin.store_file_breaks()
                except AttributeError:
                    ....

I agree that this is a problem that needs a solution. Your post gives the justification very well.  I already opened #19042 for this issue, so as is our usual policy, I am merging this duplicate into that one. 

Thank you for submitting a patch.  To apply it, we need a Contributor Agreement.  One can be signed electronically.  See https://www.python.org/psf/contrib/.  An '*' will appear after your name once a CA has been received and registered.  I will take a good look once this happens.

I the meanwhile, I will add a reference to this issue and patch, as well as additional comments, to #19042.

Thanks Terry, I tried searching for a similar issue but failed.

Feels like signing contributor form will take a while.
Meantime please feel free to tweak/improve and implement code in your way (Mine is a bit rough solution not even abiding by naming convention), if this is some licensing issue.

In my additional comment, I explored the idea of running without saving, not even to a temp file.