Many readers here know interactive Python sessions with
prompts like ">>>". But a "session" could be something else.
One could imagine that when starting a new session, one
still sees all the variables and constants defined in
preceding sessions.

I have implemented something like a "restore()" and a "save()"
call. "restore()" will restore the names from the last "save()".
"save()" will look for user-defined names (it excludes certain
standard names and certain other names from my software) and
save them using the "shelve" package from the standard library.

I you know "shelve" or have read the subject line, you can
guess what comes now:

I cannot save user-defined functions this way!

When a user types into the console:

def f():

|... print( "example" )
|...

he gives source code to shell and hopes that the shell will
cherish the memory of that function. But instead it acts as
if from now on it does not know the source code of "f"!

So, there seems to be no way now to persist this function
to a file? as if by "save( f )" or something similar?
If not the source code, then maybe some other form?

So much for the topic of "In Python, /everything/ is an
object"! There seem to be first and second-class objects:
Shelveable and non-shelveable objects.

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Wayne Harris <[email protected]> writes:

Wow. Could the dis module help at all?

Thank you for this idea! I think this should work, but only
under CPython and not necessarily across different Python
versions. Still, I might use dis.

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On 12/11/2022 10:01, Stefan Ram wrote:

Many readers here know interactive Python sessions with
prompts like ">>>". But a "session" could be something else.
One could imagine that when starting a new session, one
still sees all the variables and constants defined in
preceding sessions.

I have implemented something like a "restore()" and a "save()"
call. "restore()" will restore the names from the last "save()".
"save()" will look for user-defined names (it excludes certain
standard names and certain other names from my software) and
save them using the "shelve" package from the standard library.

I you know "shelve" or have read the subject line, you can
guess what comes now:

I cannot save user-defined functions this way!

When a user types into the console:

def f():

|... print( "example" )
|...

he gives source code to shell and hopes that the shell will
cherish the memory of that function. But instead it acts as
if from now on it does not know the source code of "f"!

So, there seems to be no way now to persist this function
to a file? as if by "save( f )" or something similar?
If not the source code, then maybe some other form?

So much for the topic of "In Python, /everything/ is an
object"! There seem to be first and second-class objects:
Shelveable and non-shelveable objects.

Wow. Could the dis module help at all? Say by getting the bytes of the compiled function and then saving them to a file, then reading them off
later and rebuilding the function with dis again?

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On 13/11/2022 05.05, Stefan Ram wrote:

Wayne Harris <[email protected]> writes:

Wow. Could the dis module help at all?

Thank you for this idea! I think this should work, but only
under CPython and not necessarily across different Python
versions. Still, I might use dis.

Was constructing a two-part tutorial. When it came to the preparing for
the second meeting, was surprised to discover that PyCharm retained code
and values in its Python Console (its REPL tab/window) - I'm presuming,
within its 'project' structure.

Was more interested in ensuring all-parties would be able to re-create
the ending/re-starting position, regardless of IDE. Accordingly, never
looked any further.

Depending upon the full range of criteria, may be worth a look...


Disclaimer: JetBrains sponsor our local PUG with a one-year 'pro'
license, as a monthly 'door prize'. Apart from using the product, have
no other connection!

Similarly, have not looked at such within VS-Codium or other editors/IDEs...
--
Regards,
=dn

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Sounds like Jupyter Notebooks: https://jupyter.org


From: Python-list <python-list-bounces+gweatherby=[email protected]> on behalf of Stefan Ram <[email protected]>
Date: Saturday, November 12, 2022 at 1:48 PM
To: [email protected] <[email protected]>
Subject: Persisting functions typed into the shell
*** Attention: This is an external email. Use caution responding, opening attachments or clicking on links. ***

Many readers here know interactive Python sessions with
prompts like ">>>". But a "session" could be something else.
One could imagine that when starting a new session, one
still sees all the variables and constants defined in
preceding sessions.

I have implemented something like a "restore()" and a "save()"
call. "restore()" will restore the names from the last "save()".
"save()" will look for user-defined names (it excludes certain
standard names and certain other names from my software) and
save them using the "shelve" package from the standard library.

I you know "shelve" or have read the subject line, you can
guess what comes now:

I cannot save user-defined functions this way!

When a user types into the console:

def f():

|... print( "example" )
|...

he gives source code to shell and hopes that the shell will
cherish the memory of that function. But instead it acts as
if from now on it does not know the source code of "f"!

So, there seems to be no way now to persist this function
to a file? as if by "save( f )" or something similar?
If not the source code, then maybe some other form?

So much for the topic of "In Python, /everything/ is an
object"! There seem to be first and second-class objects:
Shelveable and non-shelveable objects.


-- https://urldefense.com/v3/__https://mail.python.org/mailman/listinfo/python-list__;!!Cn_UX_p3!kVssvGre00pk5iMVIWUbuGXUwcZ8veRBEuSiX-VLlkRVlJoQ96fl6CZG9zQ72Hky8qqofZhhhA5qZpkneyEz4-4$<https://urldefense.com/v3/__https:/mail.python.org/mailman/listinfo/
python-list__;!!Cn_UX_p3!kVssvGre00pk5iMVIWUbuGXUwcZ8veRBEuSiX-VLlkRVlJoQ96fl6CZG9zQ72Hky8qqofZhhhA5qZpkneyEz4-4$>

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dn <[email protected]> writes:

Was constructing a two-part tutorial. When it came to the preparing for
the second meeting, was surprised to discover that PyCharm retained code
and values in its Python Console (its REPL tab/window) - I'm presuming, >within its 'project' structure.

I was already wondering whether some Python-Implementations
offer something like this.

I have started to work on a Newsreader. The first version of
the Newsreader is not to have any user interface at all. So,
the user directly calls Python functions to use the program.
The program is started in Idle and then one gets the usual
shell prompt of Idle and can excute Python code, using all
the definitions of the program.

For example, to configure the newsreader, the user creates
on object representing a newsserver:

s = newsaccount_class( "news.example.com" )

, then he can get a list of all the Python newsgroups:

s.groups( '*python*' )

. The abbreviated output is:

['comp.lang.python', 'pl.rec.humor.monty-python', ... ]

. It would be too cumbersome if the user would have to repeat
the configuration with "s = newsaccount_class( . . . )" every
time he starts the program, so I am offering a function to
save all the variables he has defined and try to find a way
to make it easy to write and save "macros" (= nothing else
than standard Python functions).

(This "zero user interface" does not exclude that at a later
date a more traditional user interface is added,
for example, via the standard package "cmd" or using tkinter.)

PS: While writing this post, by chance, I came across the
documentation of the standard package "code". This might
help me to find a way to get the source code of function
definitions if I use it to write my own shell!

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On Sun, 13 Nov 2022 at 05:48, Stefan Ram <[email protected]> wrote:

So much for the topic of "In Python, /everything/ is an
object"! There seem to be first and second-class objects:
Shelveable and non-shelveable objects.

That's a bit unfair. Everything IS an object, but not all objects can
be treated the same way. Complex numbers can't be compared for greater-than/less-than, but they are still first-class objects.

Is it acceptable to you if the reconstituted function doesn't have
source code (which will affect tracebacks and such), as long as it
behaves the same way? If so, save the __code__.co_code attribute, and
build a new function from that.

ChrisA

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[email protected] (Stefan Ram) writes:

PS: While writing this post, by chance, I came across the
documentation of the standard package "code". This might
help me to find a way to get the source code of function
definitions if I use it to write my own shell!

Session transcript and my source code below:

transcript

This Python Interpreter is now ready to accept statements.

x = 7
x

7

def f(): print( 'example' )

...

*** Function definition found: ***
def f(): print( 'example' )

f()

example

def g():

... print( 'example' )
...

*** Function definition found: ***
def g():
print( 'example' )

g()

example

main.py

import codeop
print( 'This Python Interpreter is now ready to accept statements.' )

def check_for_function_definition( listing ):
stripped = listing[ 0 ].strip()
found0 = stripped.startswith( "def" )
found1 = len( stripped )> 3 and stripped[ 3 ].strip() == ''
found = found0 and found1
if found:
print()
print( '*** Function definition found: ***' )
print( '\n'.join( listing ))
print()

class Interpreter:
def __init__( self ):
self.locals={}
self.prepare_statement()
self.mainloop()
def prepare_statement( self ):
self.listing = []
print( end='>>> ' )
self.multiline = False
def process_possible_code( self ):
code = codeop.compile_command( '\n'.join( self.listing ))
if code:
check_for_function_definition( self.listing )
lines = '\n'.join( self.listing )
exec( code, self.locals, self.locals )
self.prepare_statement()
else:
self.multiline = True
print( end='... ' )
def mainloop( self ):
while True:
line = input()
self.listing.append( line )
if self.multiline:
if line.strip() != '':
print( end='... ' )
continue
else:
self.process_possible_code()
else:
self.process_possible_code()

Interpreter()

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