Compound Logical Expression

def conditions_match(conditionlist,t):
    if isinstance(conditionlist, basestring):
        #smallest unit of work: non list. eval the expression.
        return eval(conditionlist)    
    elif len(conditionlist) == 1:
        #list is a single item, visit its content.
        return conditions_match(conditionlist[0],t)
    else:
    	#we know we have "SOMETHING AND/OR/NOT SOMETHINGS" as our input
        if conditionlist[0] is "NOT":
            return not conditions_match(conditionlist[1:],t)
        if conditionlist[1] is "AND":
            if conditionlist[2] is "NOT":
                return conditions_match(conditionlist[0],t) and not conditions_match(conditionlist[3:],t)
            else:
                return conditions_match(conditionlist[0],t) and conditions_match(conditionlist[2:],t)            
        if conditionlist[1] is "OR":
            if conditionlist[2] is "NOT":
                return conditions_match(conditionlist[0],t) or not conditions_match(conditionlist[3:],t)
            else:
                return conditions_match(conditionlist[0],t) or conditions_match(conditionlist[2:],t)

#here is an example of an expression in this grammar. The graphical interface will generate something in this format.
#Data and rule are nonsense in this case just to show the format.
conditionlist1=[["t['type']=='CAD'", "AND","t['amount']>50"],"OR",["t['type']=='USD'", "AND","NOT","t['amount']<=(100+(t['amount']/2))"]]

#here are some example transactions that we are processing to see if they match user generated ruleslen()
t1=[{'amount':45,'type' : "CAD"},
	{'amount':95,'type' : "USD"},
	{'amount':55,'type' : "CAD"},
	{'amount':105,'type' : "USD"}]

for t in t1:
    print conditions_match(conditionlist1,t)

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