Know a good pickle howto?

[spacecoyote]

I need to know how to use pickle (and its brethren) correctly. Does anyone know of a good tutorial? The python manual is a bit too dense on this subject.

[ghostdog74]

how about this ?here

[bartonc]

I need to know how to use pickle (and its brethren) correctly. Does anyone know of a good tutorial? The python manual is a bit too dense on this subject.

It's really quite simple:

>>> import cPickle
>>> strList = ['asf','dadf','adf','adf',]
>>> pickleFile = open("pickleTest.dat", "w")
>>> cPickle.dump(strList, pickleFile)
>>> pickleFile.close()
>>> pickleFile = open("pickleTest.dat")
>>> unpickledList = cPickle.load(pickleFile)
>>> print unpickledList
['asf', 'dadf', 'adf', 'adf']
>>> pickleFile.close()
>>>

[bartonc]

how about this ?here

Great Post! I'll put that link into the new sticky (actually the parent page). Thanks gd

[ghostdog74]

No prob :)

[bartonc]

No prob :)

two posts to go...

[bvdet]

I need to know how to use pickle (and its brethren) correctly. Does anyone know of a good tutorial? The python manual is a bit too dense on this subject.

We use Pickler and Unpickler in several of our applications to save and restore a dictionary or list of dictionaries.
Library functions:

import os
import macrolib.pickle
from param import Warning

def import_data(file_name):
    try:
        f = open(file_name, "r")
    except IOError, e:
        # unable to open file
        Warning("Default file import error. Reverting to original defaults...")
        return None
    
    # file open is successful
    try:
        
        dd = macrolib.pickle.Unpickler(f).load()
        f.close()
        # test for a dictionary or list of dictionaries
        if isinstance(dd, dict):
            return dd
        elif isinstance(dd, list):
            for i, item in enumerate(dd):
                if not isinstance(item, dict):
                    Warning("**INVALID** List item %s is not a dictionary." % (i))
                    return None
            # always return one dictionary
            ddr = {}
            for d in dd: ddr.update(d)
            return ddr
        else:
            # dd is not a dictionary or list of dictionaries
            Warning("Invalid imported data type.\nData must be a dictionary or list of dictionaries.")
            return None
    
    except:
        # file is not compatible with Unpickler - close file and warn user
        f.close()
        Warning("Invalid defaults file. Reverting to original defaults...")
        return None
    
def export_data(file_name, dd):
    if check_Defaults_dir(os.path.dirname(file_name)):
        # directory exists or was created
        try:
            f = open(file_name, "w")
            macrolib.pickle.Pickler(f).dump(dd)
            f.close()
            return True
        except:
            Warning("Default values file export error.")
            return False
        
    else:
        # directory did not exist and the user chose 'no' to create directory
        Warning("The default values file export was aborted")
        return False

Typical function calls:

    ## auto import defaults data if enabled
    if enable_default_import_export == "Enable":
        dd0 = import_data(os.path.join(default_file_path, def_file))
        if dd0:
            for key, value in dd0.items():
                exec "%s = %s" % (key, repr(value)) in None
            else:
                Warning("Invalid data - Reverting to original defaults")
    ## auto export default values to disk if enabled
    if enable_default_import_export == "Enable":
        export_data(os.path.join(default_file_path, def_file), dd_list)

Module pickle works with many data types. From Python Essential Reference:
"Multiple calls to the dump() and load() methods are allowed, provided that the sequence of load() calls used to restore a collection of previously stored objects matches the sequence of dump() calls during the pickling process."
HTH :-),
BV

[spacecoyote]

I figured out how to do what I wanted to do (before you guys posted :p). But I'll have a look at these.

[bartonc]

I figured out how to do what I wanted to do (before you guys posted :p). But I'll have a look at these.

Did you notice that the docs say that cPickle can be 1000 times faster than the old pickle module?