不使用Find方法从字符串中查找字符？

Question

因为我是个新手。。。不明白为什么它不能正常工作？ 期待的原因和解决办法，并提示 谢谢

str = "gram chara oi ranga matir poth"
find ='p'
l = len(str)
for x in range(0,l):
    if str[x]==find:         
        flag = x
        #break
if flag == x:
    print "found in index no",flag
else:
    print "not found in there"

Answer 1

您的搜索方法是有效的（遍历字符串中的字符）。然而，你的问题是在最后当你评估你是否找到了这个角色。你在比较flag和x，但是当你做比较时，x是out of scope。因为x是在for循环语句中声明的，所以它只在for循环中定义。因此，要修复代码，请为flag设置一个可以检查的初始值，然后更改结尾处的检查：

flag = None
for x in range(len(str)):
    if str[x] == find:         
        flag = x
        break  # Using break here means you'll find the FIRST occurrence of find 

if flag:
    print "found in index no",flag
else:
    print "not found in there"

Answer 2

if flag == x看起来很奇怪。你希望x的值是多少？你知道吗

我建议将flag初始化为None，然后在循环的末尾检查它是否不是None。你知道吗

flag = None # assign a "sentinel" value here
str = "gram chara oi ranga matir poth"
find = 'p'
for x in range(len(str)):
    if str[x] == find:         
        flag = x
        # Leaving out the break is also fine. It means you'll print the
        # index of the last occurrence of the character rather than the first.
        break
if flag is not None:
    print "found in index no", flag
else:
    print "not found in there"

Answer 3

您正试图使flag成为（第一个）匹配字符的索引位置。很好！你知道吗

if str[x]==find:
  flag = x
  break

但是如果什么也没找到怎么说呢？测试x也没用！尝试将标志初始化为可测试值：

flag = -1
for x in range(0,l):
    if str[x]==find:         
        flag = x
        break

现在一切都很简单：

if flag != -1:
    print "found in index no",flag
else:
    print "not found in there"