PyYaml Expect scalar but found Sequence

Question

I am trying to load with user defined tags in my python code, with PyYaml. Dont have much experience with pyYaml loader, constructor, representer parser, resolver and dumpers.

Below is my code what i could come up with:

import yaml, os 
from collections import OrderedDict

root = os.path.curdir

def construct_position_object(loader, suffix, node):
    return loader.construct_yaml_map(node)

def construct_position_sym(loader, node):
    return loader.construct_yaml_str(node)

yaml.add_multi_constructor(u"!Position", construct_position_object)
yaml.add_constructor(u"!Position", construct_position_sym)


def main():
    file = open('C:\calcWorkspace\\13.3.1.0\PythonTest\YamlInput\Exception_V5.yml','r')
    datafile = yaml.load_all(file) 
    for data in datafile:          


        yaml.add_representer(literal, literal_presenter)
        yaml.add_representer(OrderedDict, ordered_dict_presenter)
        d = OrderedDict(l=literal(data))
        print yaml.dump(data,  default_flow_style=False)

    print datafile.get('abcd').get('addresses')

    yaml.add_constructor('!include', include)

def include(loader, node):
    """Include another YAML file."""

    global root
    old_root = root

    filename = os.path.join(root, loader.construct_scalar(node))
    root = os.path.split(filename)[0]

    data = yaml.load(open(filename, 'r'))
    root = old_root

    return data


class literal(str): pass

def literal_presenter(dumper, data):
    return dumper.represent_scalar('tag:yaml.org,2002:str', data, style='|')


def ordered_dict_presenter(dumper, data):
    return dumper.represent_dict(data.items())


if __name__ == '__main__':
    main()

This is my Yaml file:

#sid: Position[SIK,sourceDealID,UTPI] 
sid: Position[1232546, 0634.10056718.0.1096840.0,]
ASSET_CLASS: "Derivative"
SOURCE_DEAL_ID: "0634.10056718.0.1096840.0"
INSTR_ID: "UKCM.L"
PRODUCT_TYPE_ID: 0
SOURCE_PRODUCT_TYPE: "CDS"
NOTIONAL_USD: 14.78
NOTIONAL_CCY: 
LOB:
PRODUCT_TYPE:
#GIM
UNDERLIER_INSTRUMENT_ID:
MTM_USD: 
MTM_CCY:
TRADER_SID:
SALES_PERSON_SID:
CLIENT_SPN:
CLIENT_UCN:
CLIENT_NAME:
LE: 
---
sid: Position[1258642, 0634.10056718.0.1096680.0,]
#sid: Position[1]
ASSET_CLASS: "Derivative"
SOURCE_DEAL_ID: "0634.10056718.0.1096840.0"
INSTR_ID: "UKCM.L"
PRODUCT_TYPE_ID: 0
SOURCE_PRODUCT_TYPE: "CDS"
NOTIONAL_AMT: 18.78
NOTIONAL_CCY: "USD"
LOB:
PRODUCT_TYPE:
UNDERLIER_INSTRUMENT_ID:
MTM_AMT: 
MTM_CCY:
TRADER_SID:
SALES_PERSON_SID:
CLIENT_SPN:
CLIENT_UCN:
CLIENT_NAME:
LE: 
--- 
# Excption documents to follow from here!!!

Exception:
  src_excp_id: 100001
  # CONFIGURABLE OBJECT, VALUE TO BE POPULATED RUNTIME (impact_obj COMES FROM CONFIG FILE)
  # VALUE STARTS FROM "!POSITION..." A USER DEFINED DATATYPE
  impact_obj: !Position [1232546, 0634.10056718.0.1096840.0,]
  # CONFIGURABLE OBJECT, VALUE TO BE POPULATED RUNTIME (rsn_obj COMES FROM CONFIG FILE)
  # VALUE STARTS FROM "_POSITION..." AN IDENTIFIER FOR CONFIGURABLE OBJECTS
  rsn_obj:    !Position [1258642, 0634.10056718.0.1096680.0,]
  exception_txt: "Invalid data, NULL value provided"
  severity: "High"   

Looks like my code is unable to identify the !Position user-defined data type.

Any help would be appericiated

Regards.

Answer 1

Needed to change:

def construct_position_sym(loader, node):
    return loader.construct_yaml_str(node)

to :

def construct_position_sym(loader, node):
    return loader.construct_yaml_seq(node)

Because the position object was a sequence:

!Position [something, something]

So the constructor had to be a sequence type. Works perfect!!!