passing a date to a function in python that is calling sql server

I am trying to pass date1 and date 2 to a function in python that creates a dataframe from a sql server

  import datetime as dt
  import pandas as pd
  import pyodbc
  import sqlalchemy
  from pandas import Series,DataFrame
  cnx=sqlalchemy.create_engine("mssql+pyodbc://Omnius:MainBrain1@172.31.163.135:1433/Basis?driver=/opt/microsoft/sqlncli/lib64/libsqlncli-11.0.so.1790.0")

def func1(date1,date2):
sqlquery = "select top 10000 * from Pretty_Txns where Pay_Date between '"+date1+"' and '"+date2+"'"
df=pd.read_sql(sqlquery,cnx)

When I try and call this function from ipython

  func1(dt.date(2015,05,01),dt.date(2015,05,02))

  ----> 8     sqlquery = "select top 10000 * from Pretty_Txns where Pay_Date between  '"+date1+"' and '"+date2+"'"

 TypeError: cannot concatenate 'str' and 'datetime.date' objects

How should I call the function so that I dont get the type error.