Calculations and counting in mapping

Sometimes it is needed to do calculations in mappings.
Realize that the get() functions always return strings, so these strings need to be converted.
Always convert to python's decimals, this is the only way to avoid rounding errors. More details: pythons decimal documentation

Example calculation

import decimal

def main(inn,out):
    TOTAL_AMOUNT = decimal.Decimal('0')         #initialize total amount
    for lin inn.getloop({'BOTSID':'UNH'},{'BOTSID':'LIN'}):
        amount = lin.get({'BOTSID':'LIN'},{'BOTSID':'QTY','1234':None}) 
        TOTAL_AMOUNT += decimal.Decimal(amount)   #add amount to TOTAL_AMOUNT

    #convert TOTAL_AMOUNT back to string, indicating the number of decimals to be used (precision)      
    total_amount = TOTAL_AMOUNT.quantize(decimal.Decimal('1.00'))   #2 decimals precision

Bots version 3.1 has a new method getdecimal(); code above can now be:

import decimal

def main(inn,out):
    TOTAL_AMOUNT = decimal.Decimal('0')         #initialize total amount
    for lin inn.getloop({'BOTSID':'UNH'},{'BOTSID':'LIN'}):
        TOTAL_AMOUNT += lin.getdecimal({'BOTSID':'LIN'},{'BOTSID':'QTY','1234':None})   #add amount to TOTAL_AMOUNT

    #convert TOTAL_AMOUNT back to string, indicating the number of decimals to be used (precision)      
    total_amount = TOTAL_AMOUNT.quantize(decimal.Decimal('1.00'))   #2 decimals precision

Note: the example above could be done using function getcountsum(), see below. The recipe above gives you detailed control over the calculation.

getcount()

returns the number of records in the tree or node.
typically used for UNT-count of segments.

out.getcount()
#returns the numbers of records in outmessage.

getcountoccurrences(mpath)

returns the number of records selected by mpath.
typically used to count number of LIN segments.

out.getcountoccurrences({'BOTSID':'UNH'},{'BOTSID':'LIN'}) 
#returns the numbers of LIN-records.

getcountsum(mpath)

counts the totals value as selected by mpath.
typically used to count total number of ordered articles.

out.getcountsum({'BOTSID':'UNH'},{'BOTSID':'LIN'},{'BOTSID':'QTY','C186.6063':'12','C186.6060':None}) 
#returns total number of ordered articles.