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

[Skip Montanaro]

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