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POPython - cPickle nested datetime objects
 

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  1. POPython - cPickle nested datetime objects
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    <p>I have a list of lists, each sublist looking something like this:</p> <pre><code>a = [datetime.datetime(2012, 2, 1), datetime.datetime(2012, 2, 2), 'string', 4.00] b = [datetime.datetime(2012, 3, 1), datetime.datetime(2012, 3, 4), 'another_string', 5.00] list_of_lists = [a,b] </code></pre> <p>To pickle the list:</p> <pre><code>cPickle.dump(list_of_lists, open(filename, 'wb')) #filename defined </code></pre> <p>When run, it raises:</p> <pre><code>Traceback (most recent call last): File "analyze_data.py", line 129, in &lt;module&gt; analyze_data(sys.argv[1]) #because the dump runs inside a function File "analyze_data.py", line 77, in analyze_data cPickle.dump(list_of_lists, open(filename, 'wb')) TypeError: 'datetime.datetime' object is not callable </code></pre> <p>I've replicated the error on Python 2.7.3 and 2.6.8.</p> <p>Same error/traceback with regular pickle as well. Also, print statements immediately before the cPickle.dump suggest the error occurs here and not somewhere else.</p> <p>From the <a href="http://docs.python.org/2/library/pickle.html" rel="nofollow">docs</a>, it sounds like you can cPickle nested objects, not all of which must be built-in types. Perhaps I could change all the <a href="http://docs.python.org/2/library/datetime.html" rel="nofollow">datetime</a> objects to strings. No doubt there are many ways to accomplish serializing and I could adjust the code to make the above a non-issue. However, I need to understand why it's not possible, if that indeed is the case.</p> <p>Can anyone explain why nested datetime objects are not serializable via cPickle/pickle? </p> <p>EDIT: Pickling the above data structure works fine outside a function. Inside, no dice. See below.</p> <pre><code>def analyze_data(some_id, some_date=default_date): #some_id/some_date (datetime object) defined above … #create list_of_lists … string_date = some_date.strftime('%Y%m%d') #works filename = '{0}_{1}.p'.format(some_id, string_date) #filename created fine cPickle.dump(list_of_lists, open(filename, 'wb')) #kaboom </code></pre> <p>I map this function to other data in other modules, so ideally would like to keep the pickling inside a function call. </p>
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    1. COPlease post more info - what Python version you are using, for example, because your data structures are picklable for me both under 2.7.3 and 3.3.0.
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    2. CO+1 to @t.dubrownik. And 2.5.6, and PyPy 1.9.0/2.7.2, both work fine too. And I vaguely remember bug where `from datetime import datetime` could confuse things, which I think that was fixed in 2.3 or 2.4.
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      1. USabarnert
    3. COAlso, is it actually raising that exception at the `cPickle.dump` call, as opposed to either (a) early, when you define the values, or (b) somewhere completely different, in a `cPickle.load`? Can you print a complete traceback instead of just one line, and ideally (it won't be too slow if you can use a data set this small to repro it) do so using `pickle` instead of `cPickle`?
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