source: packson3/packson/JsonTools.py@ 136

from packson.JsonTypeInfo import Id,As, getTypeWrappingInfo, getClassId
import importlib
from packson.JsonSubTypes import getSubTypes
from typing import Dict, _GenericAlias, cast, Tuple
import inspect
from inspect import _empty
from inspect import Parameter
'''
Tools that are working just with a class 
'''

def isPrimitive(clas):
    '''
    @return true if clas is primitive: int, float, etc.
    These are also the class types that can be used for dictionary keys.
    list can't be primitive because we must check the type of the list elements and 
    use the appropriate parser for them.
    '''
    return clas in (int, float, bool, str, complex, range, bytes, bytearray)

def getInitArgs( clas) -> Dict[str, object]:
    '''
    @param clas a class object that can be instantiated
    @return dict with all arguments of clas __init__ and
    their classes.
    @throws ValueError if not all args are annotated with a type.
    '''
    if not hasattr(clas, '__init__'):
        return {}
    f=getattr(clas,'__init__')
    argclasses = {name:param._annotation for name,param in inspect.signature(f).parameters.items()}
    argclasses.pop('self')
    # _empty is indicates an undefined type in the typing system.
    untyped = [ name for name,param in argclasses.items()  if param==_empty ] 
    #untyped = set(argclasses.keys()) - set(['self'])
    if len(untyped)>0:
        raise ValueError("init function of Class "+str(clas)+\
            " must have all arguments typed, but found untyped "+str(untyped))
    return argclasses

def str_to_class(fullclasspath:str)->object:
    '''
    @param fullclasspath : full path specification to a class,
    so that we can locate and load it. 
    @return a new class, loaded from the given string.
    '''
    x=fullclasspath.rfind(".")
    module_name=""
    if x>0:
        module_name=fullclasspath[0:x]
    # load the module, will raise ImportError if module cannot be loaded
    m = importlib.import_module(module_name)
    # get the class, will raise AttributeError if class cannot be found
    c = getattr(m, fullclasspath[x+1:])
    return c


def id2class(classid:str, realclasses:list):
    '''
    @param classid the class id , coming from the json
    @param use the Id
    @param realclasses the list of real classes that are allowed
    @return the real class  that has the requested id
    '''
    for clas in realclasses:
        if classid==getClassId(clas):
            return clas
    raise ValueError("There is no class with id "+ classid+" in " + str(realclasses) )

def addTypeInfo( clas, jdict:dict)->dict:
    '''
    @param clas the class of the object to be serialized
    @jdict an already json-ized object dict, but without type wrapper
    @return res, but with type info added
    '''
    (use, include) = getTypeWrappingInfo(clas)
    if use == Id.NONE:
        return jdict
    classid = getClassId(clas)
        
    if include == As.WRAPPER_OBJECT:
        return { classid:jdict }
    else:
        raise ValueError("Not implemented include type "+str(include))

        


def getActualClass(data:dict,clas)->tuple:
    '''
    @param data the json dict to be deserialized. It should contain the
    class type info.
    @param clas the expected class. This class IS annotated with jsonsubtypes but
    clas may differ from the originally annotated class (it may just have inherited the annotation)
    @return tuple (actualdata,actualclass). with the actualclass contained in the data. It must be one 
    of the classes in the __jsonsubtypes__ of class. actualdata is stripped of the type data contained
    in the original data dict. ASSUMES typewrappinginfo is set
    @throws if typewrapping info is not set.
    '''
    (use, include) = getTypeWrappingInfo(clas)

    if getSubTypes(clas):
        (_annotatedclass, subclasslist) = getSubTypes(clas)
        # we could not load the real classes earlier
        # because they did not yet exist at parse time.
        realclasses=[str_to_class(classname) for classname in subclasslist]
        realclasses.append(clas)
    else:
        # class has no subtypes annotation, it can be only the indicated class.
        realclasses=[clas]
    '''
    Algorithm: this ignores annotatedclass.
    We first try to find which of the subclasslist is actually in the data.
    Then we just check if that is subclass of clas.
    '''
    if include==As.WRAPPER_OBJECT:
        if len(data.keys())!=1:
            raise ValueError("WRAPPER_OBJECT requies 1 key (class id) but found "+str(data.keys()))
        classid = next(iter(data.keys()))
        actualdata = data[classid]
    else: 
        raise ValueError("Not implemented: deserialization with include "+str(include))

    # find back the matching full classname
    actualclas = id2class(classid, realclasses)
    
    # We found a class that matches the header.
    # but the clas requested might be more restrictive as we may be in a subclass
    #FIXME can we do this test once, somewhere, for all of the realclasses?
    if not issubclass(actualclas, clas):
        raise ValueError("The class ID ("+str(actualclas)+" is not implementing the requested class "+str(clas))
    return (actualdata, actualclas)
    
def getListClass(listofobj:set)->object:
    '''
    @param listofobj a list/set/tuple with at least 1 object
    @return class of the list elements. All elements must be same class
    @throws ValueError if that is not the case
    '''        
    if len(listofobj)==0:
        raise ValueError("bug, getListClass called with empty list")
    clas=type(next(iter(listofobj))) # object may be a list, dict, set
    for obj in listofobj:
        if not type(obj)==clas:
            raise ValueError("Expected element of type "+str(clas)+"but found "+str(obj))
    return clas