How to parse this string of data structure with pyparsing

Question

I have the following sample data that are stored in a file:

[
  { "keys": ["val1", "val2"], "args": { "arg1": "val1", "arg2": "val2" } },
  { "keys": ["val1", "val2", "val3"], "args": { "arg": "val" } },
  { "keys": ["val"], "args": {} }
]

As you may realise, this is a list of dictionaries. Each dictionary has key keys contains arbitrary length of list and key args contains a dictionary

How could I parse this sample data back into Python object

with open('file_name') as file:
    source = file.read()

data = how_to_parse(source)

for arr in data:
    print(arr)

# Expected result
# { "keys": ["val1", "val2"], "args": { "arg1": "val1", "arg2": "val2" } }
# { "keys": ["val1", "val2", "val3"], "args": { "arg": "val" } }
# { "keys": ["val"], "args": {} }

Tks @AvinashRaj, that is correct answer. However as I am trying to learn pyparsing. I'd like to see an example using that library :) — babygau
– babygau, Commented Dec 21, 2015 at 8:24
Since your data looks like being JSON-formatted you might take a look at the json module. — albert
– albert, Commented Dec 21, 2015 at 8:36

PaulMcG · Accepted Answer · 2015-12-21 16:05:30Z

1

The pyparsing wiki includes this example https://pyparsing.wikispaces.com/file/view/parsePythonValue.py/31712649/parsePythonValue.py which I implemented at a time when ast.literal_eval was not yet available. Using this code, your expression can be parsed using:

print listItem.parseString("""[
  { "keys": ["val1", "val2"], "args": { "arg1": "val1", "arg2": "val2" } },
  { "keys": ["val1", "val2", "val3"], "args": { "arg": "val" } },
  { "keys": ["val"], "args": {} }
]""")[0]

which gives:

[{'keys': ['val1', 'val2'], 'args': {'arg1': 'val1', 'arg2': 'val2'}}, 
 {'keys': ['val1', 'val2', 'val3'], 'args': {'arg': 'val'}}, 
 {'keys': ['val'], 'args': {}}]

There are many more examples at https://pyparsing.wikispaces.com/Examples for your self-edification.

answered Dec 21, 2015 at 16:05

PaulMcG

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3 Comments

PaulMcG Over a year ago

This example is explained in more detail in this presentation ptmcg.com/geo/python/confs/TxUnconf2008Pyparsing.html - mouse over the lower-right corner to see the presentation navigation icons.

babygau Over a year ago

Thank you for your answer. It's great start for me to learn pyparsing

PaulMcG Over a year ago

Pyparsing is no longer hosted on wikispaces.com. Go to github.com/pyparsing/pyparsing

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