python笔记006——函数

函数基础

计算字符串中某字符个数

 1 def countsubstring(s,ch):         #s和ch为形参
 2     c=0
 3     i=0
 4     while i<len(s):
 5         if s[i]==ch:
 6             c +=1
 7         i +=1
 8     print(c)
 9 str=‘wujiadongjiangruisuirsuiuigjsjsiuisldjsjeuiui‘
10 m=‘i’
11 countsubstring(s,m)      #调用函数传入的参数str和m为实参

计算子串sub个数

 1 def countsubstring(s,sub):
 2     c=0
 3     i=0
 4     while i<=len(s)-len(sub):
 5         if s[i:i+len(sub)]==sub:
 6             c +=1
 7 #                                  print(s[i:i+len(sub)])
 8         i +=1
 9     print(c)
10 str=‘wujiadongjiangruisuirsuiuigjsjsiuisldjsjeuiui‘
11
12 countsubstring(str,‘ui‘)

 1 def myfind(s,sub):
 2     i=0
 3     while i<=len(s)-len(sub):
 4         if s[i:i+len(sub)]==sub:
 5             print(i)
 6             break
 7         i +=1
 8     else:
 9         print(‘-1‘)
10
11 str=‘wujiadong‘
12 sub=‘on‘
13 myfind(str,sub)

找最大值

 1 li=[111,2,3,7,9,76,98,23,45]
 2 def myfindmax(M):
 3     i=0
 4     max=li[0]
 5     while i<len(li):
 6         if max<li[i]:
 7            max=li[i]
 8
 9         i +=1
10     print(max)
11 myfindmax(li)

找第二大值

#这种情况两个最大都相等时是错误的 1 li=[111,222,333,7,9,765,98,23,45]
 2 def max2(t):
 3     max1=t[0]
 4     max2=t[0]
 5     for x in t:
 6         if x >max1:
 7            max2=max1
 8            max1=x
 9         else:
10           if x >max2:              #这里添加上条件x！=max1  就可避免
11               max2=x
12     print(‘max1‘,max1)
13     print(‘max2‘,max2)
14 max2(li)

删除某个值

 #有bug，有重复的值不能删除

 1 li=[1,2,3,4,5,6,7,8,9]
 2 def delvalue(t):
 3     global  li           #没懂为什么一定要加这个
 4     i=0
 5     while i<len(li):
 6         if li[i]==t:
 7             left=li[:i]
 8             print(left)
 9             right=li[i+1:]
10  #        print(i)
11             li=left+right
12         i +=1
13
14 delvalue(6)

删除所有的值