CODEWITHSUNDEEP
pythonctypes
G.A.
G.A.

Reputation: 1523

Python: Can we convert a ctypes structure to a dictionary?

I have a ctypes structure. 

class S1 (ctypes.Structure):
    _fields_ = [
    ('A',     ctypes.c_uint16 * 10),
    ('B',     ctypes.c_uint32),
    ('C',     ctypes.c_uint32) ]

if I have X=S1(), I would like to return a dictionary out of this object: Example, if I do something like: Y = X.getdict() or Y = getdict(X), then Y might look like: 

{ 'A': [1,2,3,4,5,6,7,8,9,0], 
  'B': 56,
  'C': 8986 }

Any help ?

Upvotes: 16

Views: 10087

Answers (4)

dizcza
dizcza

Reputation: 698

In case you have arrays in fields, I extended llasram's answer:

class SerializableStruct(ctypes.Structure):
    def getattr_dict(self, name):
        def todict(a):
            return a.to_dict() if isinstance(a, SerializableStruct) else a

        attr = getattr(self, name)
        if isinstance(attr, ctypes.Array):
            return [todict(attr[i]) for i in range(len(attr))]
        return todict(attr)

    def to_dict(self):
        return dict((f, self.getattr_dict(f)) for f, _ in self._fields_)

You need to subclass SerializableStruct rather than ctypes.Structure while declaring your custom data types.

Upvotes: 0

llasram
llasram

Reputation: 4475

How about something like:

class S1(ctypes.Structure):
    _fields_ = [ ... ]

    def getdict(self):
        return dict((f, getattr(self, f)) for f, _ in self._fields_)

Upvotes: 2

Sam P
Sam P

Reputation: 721

A little bit more general purpose to handle double arrays, and arrays of structures, and bitfields.

def getdict(struct):
    result = {}
    #print struct
    def get_value(value):
         if (type(value) not in [int, float, bool]) and not bool(value):
             # it's a null pointer
             value = None
         elif hasattr(value, "_length_") and hasattr(value, "_type_"):
             # Probably an array
             #print value
             value = get_array(value)
         elif hasattr(value, "_fields_"):
             # Probably another struct
             value = getdict(value)
         return value
    def get_array(array):
        ar = []
        for value in array:
            value = get_value(value)
            ar.append(value)
        return ar
    for f  in struct._fields_:
         field = f[0]
         value = getattr(struct, field)
         # if the type is not a primitive and it evaluates to False ...
         value = get_value(value)
         result[field] = value
    return result

Upvotes: 3

Tamás
Tamás

Reputation: 48071

Probably something like this:

def getdict(struct):
    return dict((field, getattr(struct, field)) for field, _ in struct._fields_)

>>> x = S1()
>>> getdict(x)
{'A': <__main__.c_ushort_Array_10 object at 0x100490680>, 'C': 0L, 'B': 0L}

As you can see, it works with numbers but it doesn't work as nicely with arrays -- you will have to take care of converting arrays to lists yourself. A more sophisticated version that tries to convert arrays is as follows:

def getdict(struct):
    result = {}
    for field, _ in struct._fields_:
         value = getattr(struct, field)
         # if the type is not a primitive and it evaluates to False ...
         if (type(value) not in [int, long, float, bool]) and not bool(value):
             # it's a null pointer
             value = None
         elif hasattr(value, "_length_") and hasattr(value, "_type_"):
             # Probably an array
             value = list(value)
         elif hasattr(value, "_fields_"):
             # Probably another struct
             value = getdict(value)
         result[field] = value
    return result

If you have numpy and want to be able to handle multidimensional C arrays, you should add import numpy as np and change:

 value = list(value)

to:

 value = np.ctypeslib.as_array(value).tolist()

This will give you a nested list.

Upvotes: 13

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