from peewee import *
db = SqliteDatabase('mydatabase.db')

class BaseModel(Model):
   class Meta:
      database = db

class Contacts(BaseModel):
   RollNo = IntegerField()
   Name = TextField()
   City = TextField()

class Branches(BaseModel):
   RollNo = IntegerField()
   Faculty = TextField()

db.create_tables([Contacts, Branches])

#this query is used as subquery
faculty=Branches.select(Branches.RollNo).where(Branches.Faculty=="ETC")
names=Contacts.select().where (Contacts.RollNo .in_(faculty))

print ("RollNo and City for Faculty='ETC'")
for name in names:
   print ("RollNo:{} City:{}".format(name.RollNo, name.City))

db.close()

RollNo and City for Faculty='ETC'
RollNo:103 City:Indore
RollNo:104 City:Nasik
RollNo:108 City:Delhi
RollNo:110 City:Nasik