if expression ：　　if_suitelse:　　else_suit

adic={"name":"paulwinflo","age":18,"sex":"man"}if "name" in adic:    print "hello "+ adic["name"]else:    print "no this key "

if expression ：#条件一　　if_suit
elif expression1 ：#条件二
　　elif_suit
elif expression2 ：#条件三
　　elif_suit
..
..

else: #其他情况下　　
　　else_suit

num=input("please input a number:")if num > 0 :    print str(num) + " is above zero"elif num < 0:    print str(num) +  " is ablow zero"else:     print str(num) +  " is eqel zero"

while expression:    while_suit

num=input("please input a number:")while  num > 8 and num <13 :##符合条件的数进入while循环    print str(num)+" is ok"    num+=1

for a in range(7):    print a,