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Python学习笔记四:过程控制
条件语句:
#以缩进来区分表示同一范围。
1 # coding=utf8 2 # 例1:if 基本用法 3 4 flag = False 5 name = ‘luren‘ 6 if name == ‘python‘: # 判断变量否为‘python‘ 7 flag = True # 条件成立时设置标志为真 8 print ‘welcome boss‘ # 并输出欢迎信息 9 else:10 print name # 条件不成立时输出变量名称
多重判断:
1 # coding=utf8 2 # 例2:elif用法 3 4 num = 5 5 if num == 3: # 判断num的值 6 print ‘boss‘ 7 elif num == 2: 8 print ‘user‘ 9 elif num == 1:10 print ‘worker‘11 elif num < 0: # 值小于零时输出12 print ‘error‘13 else:14 print ‘roadman‘ # 条件均不成立时输出
python 并不支持 switch 语句
1 # coding=utf8 2 # 例3:if语句多个条件 3 4 num = 9 5 if num >= 0 and num <= 10: # 判断值是否在0~10之间 6 print ‘hello‘ 7 >>> hello # 输出结果 8 9 num = 1010 if num < 0 or num > 10: # 判断值是否在小于0或大于1011 print ‘hello‘12 else:13 print ‘undefine‘14 >>> undefine # 输出结果15 16 num = 817 # 判断值是否在0~5或者10~15之间18 if (num >= 0 and num <= 5) or (num >= 10 and num <= 15): 19 print ‘hello‘20 else:21 print ‘undefine‘22 >>> undefine # 输出结果
同一行,与IDL类似
1 #!/usr/bin/python 2 3 var = 100 4 5 if ( var == 100 ) : print "Value of expression is 100" 6 7 print "Good bye!"
循环语句:
while
1 #!/usr/bin/python2 3 count = 04 while (count < 9):5 print ‘The count is:‘, count6 count = count + 17 8 print "Good bye!"
while... else
1 #!/usr/bin/python2 3 count = 04 while (count < 9):5 print ‘The count is:‘, count6 count = count + 17 8 print "Good bye!"
1 #!/usr/bin/python2 3 flag = 14 5 while (flag): print ‘Given flag is really true!‘6 7 print "Good bye!"
while循环嵌套
1 #coding=utf-8 2 #!/usr/bin/python 3 4 i = 2 5 while(i < 100): 6 j = 2 7 while(j <= (i/j)): 8 if not(i%j): break 9 j = j + 110 if (j > i/j) : print i, " 是素数"11 i = i + 112 13 print "Good bye!"
for
遍历任何序列的项目,列表或字符串
for i in sequence
statements(s)
1 #!/usr/bin/python 2 3 for letter in ‘Python‘: # First Example 4 print ‘Current Letter :‘, letter 5 6 fruits = [‘banana‘, ‘apple‘, ‘mango‘] 7 for fruit in fruits: # Second Example 8 print ‘Current fruit :‘, fruit 9 10 print "Good bye!"
>
Current Letter : PCurrent Letter : yCurrent Letter : tCurrent Letter : hCurrent Letter : oCurrent Letter : nCurrent fruit : bananaCurrent fruit : appleCurrent fruit : mangoGood bye!
索引
1 #!/usr/bin/python2 3 fruits = [‘banana‘, ‘apple‘, ‘mango‘]4 for index in range(len(fruits)):5 print ‘Current fruit :‘, fruits[index]6 7 print "Good bye!"
内置函数 len() 和 range(),函数 len() 返回列表的长度,即元素的个数。 range返回一个序列的数。
for.... else...(for循环嵌套)
1 #!/usr/bin/python 2 3 for num in range(10,20): #to iterate between 10 to 20 4 for i in range(2,num): #to iterate on the factors of the number 5 if num%i == 0: #to determine the first factor 6 j=num/i #to calculate the second factor 7 print ‘%d equals %d * %d‘ % (num,i,j) 8 break #to move to the next number, the #first FOR 9 else: # else part of the loop10 print num, ‘is a prime number‘
break跳出整个循环 continue跳出本次循环 pass空语句,是为了保持程序结构的完整性。
1 #!/usr/bin/python2 3 for letter in ‘Python‘: 4 if letter == ‘h‘:5 pass6 print ‘This is pass block‘7 print ‘Current Letter :‘, letter8 9 print "Good bye!"
Python学习笔记四:过程控制
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