Python基础02.条件与循环

Python基础02.条件与循环

Python3.7条件语句

1、条件语句

（1）if else 语句

    if 判断语句：
        执行语句     #成立执行
        .....
    else:
        .....       #不成立时执行

a=5
if a%2==0:
    print(a,"是偶数")
else:
    print(a,"是奇数")    #a是奇数

（2）if elif else 语句

  if 判断语句1:
      执行语句1
  elif 判断语句2:
      执行语句2
  elif 判断语句3:
      执行语句3
  else:
      执行语句

a=5
if a<0 :
    print(a,"是负数")
elif a>=0 and a%2==0:
    print(a,"是正偶数")
elif a>=0 and a%2==1:
    print(a,"是整奇数")
else:
    print("erro")

2、循环语句

（1）while循环语句

    while 判断语句：
         执行语句
         ......

numbers=[12,32,-76,9,-23,-10]
Positive=[]
negative=[]
while(len(numbers)>0):
    number=numbers.pop()
    if number>0:
        Positive.append(number)
    if number<0:
        negative.append(number)
print("Positive=",Positive,"negative=",negative)
#Positive= [9, 32, 12] negative= [-10, -23, -76]

（2）for循环语句

for iterating_var in sequence:     #sequence可为列表或元组
   statements(s)

list1=['a','b','c','d']     #list1=('a','b','c','d')
for i in range(len(list1)):
    print (list1[i])]

（3）嵌套循环
for嵌套：

for iterating_var in sequence:
   for iterating_var in sequence:
      statements(s)
   statements(s)

while嵌套：

while expression:
    while expression:
        statement(s)
    statement(s)

for-while 混合嵌套

（4）break语句

for num in range(0,5):
    print(num)
    if num==3:
        break      #0 1 2 3

（5）continue语句

for num in range(0,5):
    if num==3:
       continue
    print(num)     #0 1 2 4