Python快速上手之流程控制语法（day2）

Python流程控制语法
if语句

var1 = 100
if var1:
   print "1 - Got a true expression value"
   print var1

var2 = 0
if var2:
   print "2 - Got a true expression value"
   print var2
print "Good bye!"

#if的条件可以是数字或字符串或者布尔值True和False（布尔表达式）
#如果是数字，则只要不等于0，就为true
#如果是字符串，则只要不是空串，就为true

if else

var = 100
if var == 200:
   print "1 - Got a true expression value"
   print var
elif var == 150:
   print "2 - Got a true expression value"
   print var
elif var == 100:
   print "3 - Got a true expression value"
   print var
else:
   print "4 - Got a false expression value"
   print var

print "Good bye!"

嵌套if else

var = 100
if var < 200:
   print "Expression value is less than 200"
   if var == 150:
      print "Which is 150"
   elif var == 100:
      print "Which is 100"
   elif var == 50:
      print "Which is 50"
elif var < 50:
   print "Expression value is less than 50"
else:
   print "Could not find true expression"

print "Good bye!"

while循环

count = 0
while count < 5:
   print count, " is  less than 5"
   count = count + 1
else:
   print count, " is not less than 5"

x=2
i=0
while x<34:
    i+=1
    if i==12:
        print "break....................................."
        break;
    print x
x=35
i=0
while x<34:
    i+=1
    if i==12:
        print "break....................................."
        break;
    print x
else:
    print "没有执行循环......."

for循环

for i in range(0,5):
    print i;
for i in range(0,5,1):
    print i;
for i in range(5,0,-1):
    print i;

#遍历集合

r=range(10,20)
r={1,2,3,4,5}    #set类型
r=["aaa",3,"c"]
print(r)
for num in r:
    print(num)


r={"a":9,"b":10}
print(r)
for num in r.values():
    print(num)