How do I serialize a Python dictionary into a string and then back to a dictionary

Question

How do I serialize a Python dictionary into a string  and then back to a dictionary  The dictionary will have lists and other dictionaries inside it

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Use Python s json module  or simplejson if you don t have python 2 6 or higher

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One thing json cannot do is dict indexed with numerals  The following snippet import json dictionary   dict  0 0  1 5  2 10   serialized   json dumps dictionary  unpacked     json loads serialized  print unpacked 0    will throw KeyError  0  Because keys are converted to strings  cPickle preserves the numeric type and the unpacked dict can be used right away

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Pickle is great but I think it s worth mentioning literal eval from the ast module for an even lighter weight solution if you re only serializing basic python types  It s basically a  safe  version of the notorious eval function that only allows evaluation of basic python types as opposed to any valid python code   Example    gt  gt  gt  d       gt  gt  gt  d 0    range 10   gt  gt  gt  d  1         gt  gt  gt  d  1   0    range 10   gt  gt  gt  d  1   1     hello   gt  gt  gt  data string   str d   gt  gt  gt  print data string  0   0  1  2  3  4  5  6  7  8  9    1    0   0  1  2  3  4  5  6  7  8  9   1   hello      gt  gt  gt  from ast import literal eval  gt  gt  gt  d    literal eval data string  True   One benefit is that the serialized data is just python code  so it s very human friendly  Compare it to what you would get with pickle dumps    gt  gt  gt  import pickle  gt  gt  gt  print pickle dumps d   dp0 I0  lp1 I0 aI1 aI2 aI3 aI4 aI5 aI6 aI7 aI8 aI9 asS 1  p2  dp3 I0  lp4 I0 aI1 aI2 aI3 aI4 aI5 aI6 aI7 aI8 aI9 asI1 S hello  p5 ss    The downside is that as soon as the the data includes a type that is not supported by literal ast you ll have to transition to something else like pickling

User · Answer

It depends on what you re wanting to use it for  If you re just trying to save it  you should use pickle  or  if you   re using CPython 2 x  cPickle  which is faster     gt  gt  gt  import pickle  gt  gt  gt  pickle dumps   foo    bar    b  x80 x03 q x00X x03 x00 x00 x00fooq x01X x03 x00 x00 x00barq x02s    gt  gt  gt  pickle loads      foo    bar     If you want it to be readable  you could use json    gt  gt  gt  import json  gt  gt  gt  json dumps   foo    bar       foo    bar     gt  gt  gt  json loads      foo    bar     json is  however  very limited in what it will support  while pickle can be used for arbitrary objects  if it doesn t work automatically  the class can define   getstate   to specify precisely how it should be pickled     gt  gt  gt  pickle dumps object    b  x80 x03cbuiltins nobject nq x00  x81q x01    gt  gt  gt  json dumps object    Traceback  most recent call last         TypeError   lt object object at 0x7fa0348230c0 gt  is not JSON serializable

User · Answer

While not strictly serialization  json may be reasonable approach here  That will handled nested dicts and lists  and data as long as your data is  simple   strings  and basic numeric types

User · Answer

If you fully trust the string and don t care about python injection attacks then this is very simple solution   d      method     eval    safe    False   guarantees    None   s   str d  d2   eval s  for k in d2      print k     d2 k    If you re more safety conscious then ast literal eval is a better bet

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If you are trying to only serialize then pprint may also be a good option  It requires the object to be serialized and a file stream   Here s some code   from pprint import pprint my dict    1  a  2  b   with open  test results txt   wb   as f      pprint my dict f    I am not sure if we can deserialize easily  I was using json to serialize and deserialze earlier which works correctly in most cases   f write json dumps my dict  sort keys   True  indent   2  ensure ascii True     However  in one particular case  there were some errors writing non-unicode data to json

User · Answer

pyyaml should also be mentioned here  It is both human readable and can serialize any python object  pyyaml is hosted here   https   bitbucket org xi pyyaml

[python] How do I serialize a Python dictionary into a string, and then back to a dictionary?

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