Shenpen

#"Project" name: PyNQ
#IDEA:
#LiNQ in C# is cool
#Python doesn't quite need it as it has generatior expressions, sum(), len(), sorted() and itertools.groupby()
#so let's just wrap a nice SQL-like interface over them in order to make them easier to use

#Problem: all these lambdas suck. Any better ways to do it?

#TODOS:
#DISTINCT (just a special case of GroupBy)
#make Select accept multiple parameters

#UPDATE 11/02/09 : better version with GroupBy() and less lambdas

from itertools import groupby

class From(object):
    def __init__(self, lst):
        self.lst = (x for x in lst)
        self.Sum = self.SimpleSum
        self.Count = self.SimpleCount

    def Where(self, func):
        self.lst = ( x for x in self.lst if func(x))
        return self

    def Select(self, func=lambda x: x):
        self.lst = (func(x) for x in self.lst)
        return self

    def SimpleCount(self, func=lambda x: x):
        return len([func(x) for x in self.lst])

    def SimpleSum(self,func=lambda x: x):
        return sum(func(x) for x in self.lst)

    def OrderBy(self, func):
        self.lst= sorted(self.lst, lambda x, y: cmp(func(x), func(y)) )
        return self

    def GroupBy(self, func):
        self.lst = groupby(sorted(self.lst,key=func),func)
        self.Sum = self.GroupedSum
        self.Count = self.GroupedCount
        return self

    def GroupedSum(self, func):
        self.lst = ( (key, sum(func(x) for x in groups) ) for key, groups in self.lst)
        return self

    def GroupedCount(self, func=lambda x: x):
        self.lst = ( (key, len([ func(x) for x in groups] )) for key, groups in self.lst)
        return self


    def __iter__(self):
        return self.lst

#EXAMPLE

sales =     (('Scotland', 'Edinburgh', 20000),
             ('Scotland', 'Glasgow', 12500),
             ('England', 'London', 90000),
             ('Wales', 'Cardiff', 29700),
             ('Wales', 'Bangor', 12800),
             ('England', 'London', 90000),
             ('England', 'London', 90000),
             ('England', 'Manchester', 45600),
             ('England', 'Liverpool', 29700))

from operator import itemgetter as column

#SELECT City, SUM(Sales)) FROM sales WHERE Country<>"Wales" GROUP BY City
myLst = From(sales)\
        .Where(lambda col: col[0] != 'Wales')\
        .GroupBy(column(1))\
        .Sum(column(2))

for x in myLst: print x