parsing a dictionary from a string

[Paul McGuire]

"Benjamin Georgi" <georgi at molgen.mpg.de> wrote in message 
news:mailman.1655.1166194994.32031.python-list at python.org...
> Hello list,
>
> I could use some help extracting the keys/values of a list of dictionaries 
> from a string that is just the str() representation of the list (the 
> problem is related to some flat file format I'm using for file IO).
>
> Example:
> >>> s = str(dict_list)
> >>> s
> '[{0: [2], 1: []}, {0: [], 1: [], 2: []}, {0: [1, 2]}]'
>
Pyparsing comes with a working example that will parse strings representing 
lists, even if they are nested.  This is actually more complex than the 
example you've given - none of your lists is nested.  Here is that example, 
adapted to handle dict elements, too.

-- Paul
(The pyparsing home page/wiki is at pyparsing.wikispaces.com.)


from pyparsing import *

cvtInt = lambda toks: int(toks[0])
cvtReal = lambda toks: float(toks[0])
cvtTuple = lambda toks : tuple(toks.asList())
cvtDict = lambda toks: dict(toks.asList())

# define punctuation as suppressed literals
lparen,rparen,lbrack,rbrack,lbrace,rbrace,colon = \
    map(Suppress,"()[]{}:")

integer = Combine(Optional(oneOf("+ -")) + Word(nums))\
    .setName("integer")\
    .setParseAction( cvtInt )
real = Combine(Optional(oneOf("+ -")) + Word(nums) + "." +
               Optional(Word(nums)))\
    .setName("real")\
    .setParseAction( cvtReal )
tupleStr = Forward()
listStr = Forward()
dictStr = Forward()

listItem = real|integer|quotedString.setParseAction(removeQuotes)| \
            Group(listStr) | tupleStr | dictStr

tupleStr << ( Suppress("(") + Optional(delimitedList(listItem)) +
            Optional(Suppress(",")) + Suppress(")") )
tupleStr.setParseAction( cvtTuple )

listStr << (lbrack + Optional(delimitedList(listItem) +
            Optional(Suppress(","))) + rbrack)

dictEntry = Group( listItem + colon + listItem )
dictStr << (lbrace + Optional(delimitedList(dictEntry) + \
    Optional(Suppress(","))) + rbrace)
dictStr.setParseAction( cvtDict )

tests = """['a', 100, ('A', [101,102]), 3.14, [ +2.718, 'xyzzy', -1.414] ]
           [{0: [2], 1: []}, {0: [], 1: [], 2: []}, {0: [1, 2]}]"""

for test in tests.split("\n"):
    print "Test:", test.strip()
    result = listStr.parseString(test)
    print "Result:", result
    for dd in result:
        if isinstance(dd,dict): print dd.items()
    print



Prints:
Test: ['a', 100, ('A', [101,102]), 3.14, [ +2.718, 'xyzzy', -1.414] ]
Result: ['a', 100, ('A', [101, 102]), 3.1400000000000001, [2.718, 
'xyzzy', -1.4139999999999999]]

Test: [{0: [2], 1: []}, {0: [], 1: [], 2: []}, {0: [1, 2]}]
Result: [{0: [2], 1: []}, {0: [], 1: [], 2: []}, {0: [1, 2]}]
[(0, [2]), (1, [])]
[(0, []), (1, []), (2, [])]
[(0, [1, 2])]