pickle unable to load collection

[Peter Otten]

paragk wrote:

> Hi,
> 
> I am unable to figure out the cause of python pickle unable to find
> the collection module.
> 
> I am getting
> 
>     __import__(module)
> ImportError: No module named collections
> 
> when I try to load a pickled object.
> 
> Details:
> 
> Python version:
> 
> Python 2.6 (r26:66721, Oct  2 2008, 11:35:03) [MSC v.1500 32 bit
> (Intel)] on win32
> 
> 
> [CODE]
> 
> import sys
> import glob
> import collections
> import pickle
> 
> ...
> 
> SomeListDict = collections.defaultdict(list)
> 
> ... # Populate SomeListDict
> 
> DictFile = open (options.saveDict, 'w')
> pickle.dump(SomeListDict , DictFile, -1)
> DictFile.close()

[...]

> From the above analysis, clearly the collection module exists, since
> the dump works.
> 
> What am I missing?

You have to open the file in binary mode "wb".

>>> import collections
>>> import pickle
>>> data = pickle.dumps(collections.defaultdict())
>>> pickle.loads(data)
defaultdict(None, {})

Now simulate the effect of writing in text mode and reading in binary mode:

>>> garbled_data = data.replace("\n", "\r\n")
>>> pickle.loads(garbled_data)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.6/pickle.py", line 1374, in loads
    return Unpickler(file).load()
  File "/usr/lib/python2.6/pickle.py", line 858, in load
    dispatch[key](self)
  File "/usr/lib/python2.6/pickle.py", line 1090, in load_global
    klass = self.find_class(module, name)
  File "/usr/lib/python2.6/pickle.py", line 1124, in find_class
    __import__(module)
ImportError: No module named collections

>>> try: pickle.loads(garbled_data)
... except ImportError as e:
...     e
...
ImportError('No module named collections\r',)

So as Steven suspected there was a whitespace char in the module name: 
pickle.load() was looking for the "collections\r" module.

Peter