以可读格式在python中腌制字典

Question

I have a python dictionary in a file in a format like this:

(dp0 S'Test' p1 S'Test1' p2 sS'Test2' p3 S'Test2' p4 sS'Starspy' p5 S'SHSN4N' p6 s.

see: Save a dictionary to a file (alternative to pickle) in Python?

and I want to read it back.

According to the question in the link, this has been created saving it with pickle. But, when I try to save a dictionary with pickle the format that I obtain does not correspond.

For example, the code:

import pickle
mydict = {'a': 1, 'b': 2, 'c': 3}
output = open('myfile.dict', 'wb')
pickle.dump(mydict, output)
output.close()

produces a file with the content

€}q (X aqKX bqKX cqKu.

I can read it back OK, but it has not the format of my file (that correspond to a nested dictionary). So, I have two questions:

First, how can I write a file with the format ... (dp0 S'Test' p1 S'Test1' p2 sS'Test2' p3 S'Test2' p4 sS'Starspy' p5 S'SHSN4N' p6 s. ?

Second, how can I read a file with that format?

Answer 1

如果你想要可读的字典，那么使用json它内置在 python 中，输出非常像字典。

Answer 2

The question is answered in the pickle module documentation: https://docs.python.org/2/library/pickle.html#data-stream-format

There are currently 3 different protocols which can be used for pickling.

Protocol version 0 is the original ASCII protocol and is backwards compatible with earlier versions of Python.

Protocol version 1 is the old binary format which is also compatible with earlier versions of Python.

Protocol version 2 was introduced in Python 2.3. It provides much more efficient pickling of new-style classes.

Whatever you show in the beginning, it the protocol version 0, and is the default. In the end — the binary protocol versions 1 or 2.

Just specify the protocol version number:

>>> pickle.dump({'hello': 'world'}, file('f.txt', 'wt'))
>>> file('f.txt', 'rt').read()
"(dp0\nS'hello'\np1\nS'world'\np2\ns."

>>> pickle.dump({'hello': 'world'}, file('f.txt', 'wt'), 2)
>>> file('f.txt', 'rt').read()
'\x80\x02}q\x00U\x05helloq\x01U\x05worldq\x02s.'

>>> pickle.dump({'hello': 'world'}, file('f.txt', 'wt'), 1)
>>> file('f.txt', 'rt').read()
'}q\x00U\x05helloq\x01U\x05worldq\x02s.'

PS: Why not just use a readable format, eg json?

Answer 3

The issue I have was a problem of versions. I was using version 3 and it works with version 2.

In that case, I can create a file with the format I have in the file I want to read, and I can now read it.