Python convert string object into dictionary

Question

I have been working to build a complex data structure which would return a dictionary. Currently that class return string object of the form

{
   cset : x,    
   b1   : y,
   b2   : z,    
   dep  : {    
              cset : x1,
              b1   : y1,    
              b2   : z1,    
              dep  : {    
                         cset : x2,     
                         b1   : y2,    
                         b2   : z2,    
                         dep  : <same as above.it  recurses few more levels>                         
                         ...  
                     }
        }
    }

I want to convert this whole string object into dictionary. I read on one of the articles to use pickle module, but I don't want to serialize it into some file and use it.

Ref : http://bytes.com/topic/python/answers/36059-convert-dictionary-string-vice-versa

I am looking for some other neater ways of doing it, if possible.

Would be great to know any such ways.

Pro tip #1: Go back and accept answers to your previous questions to avoid looking like a jerk. (The check mark is next to the reply that best answers your question) — Wayne Werner
– Wayne Werner, Commented Jul 14, 2010 at 18:54
@Wayne : I did that, didn't know about that earlier, Thank you — daydreamer
– daydreamer, Commented Jul 14, 2010 at 19:20

MAK · Accepted Answer · 2010-07-14 19:54:46Z

Don't use eval. If you are sure that the string will always contain a valid Python dict, use ast.literal_eval. This works pretty much like eval, but it only evaluates if the expression is a valid dict,list, etc. and throws an exceptions if it isn't. This is way safer than trying to evaluate strings that may contain arbitrary code at runtime.

From the docs:

Safely evaluate an expression node or a string containing a Python expression. The string or node provided may only consist of the following Python literal structures: strings, numbers, tuples, lists, dicts, booleans, and None.

This can be used for safely evaluating strings containing Python expressions from untrusted sources without the need to parse the values oneself.

Code Example:

>>> import ast
>>> ast.literal_eval("1+1")
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/usr/lib/python2.6/ast.py", line 68, in literal_eval
    return _convert(node_or_string)
  File "/usr/lib/python2.6/ast.py", line 67, in _convert
    raise ValueError('malformed string')
ValueError: malformed string
>>> ast.literal_eval("\"1+1\"")
'1+1'
>>> ast.literal_eval("{'a': 2, 'b': 3, 3:'xyz'}")
{'a': 2, 3: 'xyz', 'b': 3}

Donald Miner · Accepted Answer · 2010-07-14 18:45:47Z

1

If you are careful enough to keep the code valid python, you could use eval:

eval(yourlongstring)

answered Jul 14, 2010 at 18:45

Donald Miner

40.1k10 gold badges99 silver badges118 bronze badges

Comments

Daniel Roseman · Accepted Answer · 2010-07-14 18:57:41Z

0

Is that the actual data format? Do you have any flexibility?

It's very nearly JSON, which is a standard data format for which Python has native libraries for reading and writing (serialising and deserialising). However, to make it valid JSON both the keys and values would need to be surrounded by quotes:

"cset" : "x",
"b1"   : "y"

and so on.

answered Jul 14, 2010 at 18:57

Daniel Roseman

602k68 gold badges910 silver badges923 bronze badges

Comments

eruciform · Accepted Answer · 2010-07-14 18:49:04Z

-1

You probably do want to use Pickle:

http://docs.python.org/library/pickle.html#pickle.dumps

It can also return the value as a string, rather than writing to a file.

answered Jul 14, 2010 at 18:49

eruciform

7,7561 gold badge38 silver badges48 bronze badges

2 Comments

eruciform Over a year ago

always better to use standard libraries if possible!

user1176501 Over a year ago

isnt ast module part of the standard library now ?

Collectives™ on Stack Overflow

Python convert string object into dictionary

4 Answers 4

Comments

Comments

Comments

2 Comments

Your Answer

Linked

Hot Network Questions

Collectives™ on Stack Overflow

4 Answers 4

Comments

Comments

Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Linked

Related