Python Client - ItemUpdate.getValue() method very slow to retrieve value

cpp_lightstreamer

When I try to retrieve the value from the values from an update using the getValue() method, using line_profiler, the time spent doing it seems to take a while (time for each line is in microseconds). I would think to the time taken retrieve the values of 'BID' and 'OFR' would be tiny, and would be similar to the method getItemName(). But we can see that that the response for getValue() is _200us vs getItemName is 3us. Why is this so? line_profiler results:

Total time: 0.104478 s
File: C:\Users\User\Documents\python_scripts\project\api_calls.py
Function: onItemUpdate at line 135

Line #      Hits         Time  Per Hit   % Time  Line Contents
==============================================================
   135                                               @profile
   136                                               def onItemUpdate(self, update: ItemUpdate, *args):
   137                                                   
   138       153        459.3      3.0      0.4          epic_name = update.getItemName()
   139                                                   
   140       153        214.4      1.4      0.2          _, instrument_id, _ = epic_name.split(':')
   141       153        164.9      1.1      0.2          epic = self.info_dict[instrument_id]
   142                                           
   143                                                   
   144       153      40306.5    263.4     38.6          timestamp = update.getValue('UTM')
   145       153      33043.6    216.0     31.6          bid = update.getValue('BID')
   146       153      27661.0    180.8     26.5          ask = update.getValue('OFR')
   147                                           
   148       153        358.8      2.3      0.3          ts = float(timestamp) / 1e3
   149       153        126.7      0.8      0.1          bid = float(bid)
   150       139         42.4      0.3      0.0          ask = float(ask)
   151                                                       
   152       139         68.9      0.5      0.1          mid_price = (bid + ask) / 2
   153                                           
   154                                                   
   155                                           
   156       139       2031.1     14.6      1.9          self.q.put((epic, ts, mid_price, bid, ask))

The code I am using is:

from lightstreamer.client import (Subscription,
                                  SubscriptionListener,
                                  ItemUpdate)

class MarketListener(SubscriptionListener):
    def __init__(self, q, info_dict={}):
        super().__init__()
        self.q = q
        self.info_dict = info_dict
        
    @profile
    def onItemUpdate(self, update: ItemUpdate, *args):
        
        epic_name = update.getItemName()
        
        _, instrument_id, _ = epic_name.split(':')
        epic = self.info_dict[instrument_id]

        
        timestamp = update.getValue('UTM')
        bid = update.getValue('BID')
        ask = update.getValue('OFR')

        ts = float(timestamp) / 1e3
        bid = float(bid)
        ask = float(ask)
            
        mid_price = (bid + ask) / 2
        self.q.put((epic, ts, mid_price, bid, ask))

Alessandro.Carioni

The getItemName method simply returns the value of a variable. In contrast, getValue performs two operations: it converts the field name into a numeric index and then searches for this index in the map of the current update's values.
If performance is a concern, you can use getValue by directly passing the index position of the field as declared in the subscription field list.

cpp_lightstreamer

Alessandro.Carioni

I have tried to index via [] and methods like getValuePos(0) but the response is just None even though I can get a value from getValue("BID") from the same response.

    market_subscription = Subscription(mode="DISTINCT",
                                       items=[f"CHART:{ticker}:TICK" for ticker in tickers],
                                       fields=["BID", "OFR", "UTM"])
class MarketListener(SubscriptionListener):
    def __init__(self, q, info_dict={}):
        super().__init__()
        self.q = q
        self.info_dict = info_dict
        
    @profile
    def onItemUpdate(self, update: ItemUpdate, *args):
        
        epic_name = update.getItemName()
        
        _, instrument_id, _ = epic_name.split(':')
        epic = self.info_dict[instrument_id]
        timestamp = update.getValue('UTM')

        print("New Response")
        print("getValue:")
        bid = update.getValue('BID')
        print(bid)   # Gives float output and is correct 
        print("getValuePos:")
        bid = update.getValuePos(0)
        print(bid)   # prints blanks (is None)

The listed methods for the update (ItemUpdate) are:

['__class__', '__delattr__', '__dir__', '__doc__', '__eq__', '__format__', '__ge__', '__getattribute__', '__getstate__', '__gt__', '__hash__', '__init__', '__init_subclass__', '__le__', '__lt__', '__module__', '__ne__', '__new__', '__reduce__', '__reduce_ex__', '__repr__', '__setattr__', '__sizeof__', '__slots__', '__str__', '__subclasshook__', '_getValueAsJSONPatchIfAvailable', '_hx_class', '_hx_class_name', '_hx_fields', '_hx_interfaces', '_hx_is_interface', '_hx_methods', '_hx_statics', '_hx_super', 'getChangedFields', 'getChangedFieldsByPosition', 'getFieldIdxFromName', 'getFieldNameOrNullFromIdx', 'getFields', 'getFieldsByPosition', 'getItemName', 'getItemPos', 'getValue', 'getValueAsJSONPatchIfAvailable', 'getValueName', 'getValuePos', 'isSnapshot', 'isValueChanged', 'isValueChangedName', 'isValueChangedPos', 'm_changedFields', 'm_fields', 'm_isSnapshot', 'm_itemIdx', 'm_items', 'm_jsonPatches', 'm_nFields', 'm_newValues', 'toString']

typical output:

New Response
getValue:
5933.83
getValuePos:
New Response
getValue:
None
getValuePos:
New Response
getValue:
5934.08
getValuePos:
New Response
getValue:
None
getValuePos:
New Response
getValue:
5933.95
getValuePos:
New Response
getValue:
5933.83
getValuePos:
New Response
getValue:
5933.95
getValuePos:
New Response
getValue:
5934.08

Alessandro.Carioni

You have to use the getValue method passing an 1-based index (e.g. update.getValue(1) to retrieve the first field).
On the other hand, getValuePos is an internal method and should not be used.

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