[Python-Dev] save()/load() (original) (raw)

Skip Montanaro skip at pobox.com
Mon Dec 1 15:35:33 EST 2003

I lost the original thread, but my first thought was to use the readline module's history capability to save and reload a "session". This hack partially works for what little testing I've done (place it in sitecustomize.py):

import readline
import os
import sys

_start_len = len(open(os.path.expanduser("~/.pyhist")).readlines())

_session_file = os.path.expanduser("~/.pysession")

def save(f=_session_file, start=_start_len):
    sf = open(f, 'w')
    while True:
        line = readline.get_history_item(start)
        start += 1
        if line is None:
            break
        if line.startswith('save(') or line.startswith('load('):
            continue
        sf.write(line+"\n")

def load(f=_session_file):
    execfile(f, sys._getframe(-1).f_globals)

import __builtin__
__builtin__.save = save
__builtin__.load = load

My readline history is stored in ~/.pyhist. I can't use readline.get_history_length() to mark the start of a session for reasons which are not obvious to me. When I first started futzing around with it, readline.get_history_length() returned 9934. Now, even though my ~/.pyhist file has more than 9960 lines, get_history_length() seems to always return -1, thus making it useless in this context.

Here's a simple session showing save() and load() within the same session:

>>> import math
>>> print math.sin(47)
0.123573122745
>>> def f():
...   return math.sin(48)
... 
>>> save()
>>> load()
0.123573122745
>>> f
<function f at 0x431830>
>>> f()
-0.76825466132366682

Note that f may not be a new f, however. A call to load() in a fresh session fails to place 'f' in the session's globals. I'm not sure why. Any ideas?

Skip

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