def main():
customer = Relation(Schema("Customer", "id, fname, lname, age, height"))
customer.add(id=18392, fname="Frank", lname="Smith", age=45, height="5'8")
customer.add(id=48921, fname="Jane", lname="Doe", age=42, height="5'6")
print(customer)
# output:
#
# Customer
# id fname lname age height
# 48921 Jane Doe 42 5'6
# 18392 Frank Smith 45 5'8
print()
print(Pi["fname", "id"](customer))
# output:
#
# Customer__fname_id
# fname id
# Frank 18392
# Jane 48921
print()
print(Sigma[lambda tup: tup.age > 43](customer))
# output:
#
# Customer
# id fname lname age height
# 18392 Frank Smith 45 5'8
print()
print(Rho["MySchema"](Pi["fname", "id"](customer)))
def getRelation(table, fromName, toName):
""" 读取关系对照表
"""
relation = Relation(fromName, toName)
for line in sopen(table):
if line.startswith('#'):
continue
flds = line.rstrip().split()
chs = flds[0]
for cht in flds[1:]:
relation.add(chs, cht)
return relation
