Smiley 4321 wrote:
> If I have a sample python code to be executed on Linux. How should I
> handle multiple objects with 'pickle' as below -
>
> -------
> #!/usr/bin/python
>
> import pickle
>
> #my_list = {'a': 'Apple', 'b': 'Mango', 'c': 'Orange', 'd': 'Pineapple'}
> #my_list = ('Apple', 'Mango', 'Orange', 'Pineapple')
> my_list = ['Apple', 'Mango', 'Orange', 'Pineapple']
> #my_list = ()
> output = open('readfile.pkl', 'wb')
> pickle.dump(my_list, output)
> output.close()
>
> my_file = open('readfile.pkl', 'rb')
> my_list2 = pickle.load(my_file)
> my_file.close()
>
> print my_list
> print my_list2
> -----
>
> This code works fine but now I have to handle multiple objects?
You never do that with pickle. You pack your data into a single object
before you store it, and unpack it after loading it. Here's an example using
a tuple as the container:
fruit = ["apple", "orange"]
vegetables = ["potato", "tomato"]
beverages = ["milk", "coffee", "water"]
with open("tmp.pickle", "wb") as f:
pickle.dump((fruit, vegetables, beverages), f)
with open("tmp.pickle", "rb") as f:
fruit, vegetables, beverages = pickle.load(f)
print fruit
print vegetables
print beverages
This is however a bit errorprone. If you accidentally write the loading code
as
fruit, beverages, vegetables = pickle.load(f)
you'll end up drinking potatoes. A better container would be a dict.
Something like
pickle.dump(dict(fruit=fruit, vegetables=vegetables, beverages=beverages),
f)
...
data = pickle.load(f)
fruit = data["fruit"]
beverages = data["beverages"]
vegetables = data["vegetables"]
is harder to get wrong. It is also easier to extend. Code that only reads
the pickle will happily ignore extra keys in the dictionary. If you follow
that path somewhat more you will probably drop the lowlevel pickle and use a
key-value store like Python's shelve instead, see
http://docs.python.org/library/shelve.html
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