封装系统内置功能的函数（字符串）

def myLower(src):
    src1 = ''
    for i in src:
        if 'A' <= i <= 'Z':
            src1 += chr(ord(i) + 32)
        else:
            src1 += i
    return src1
#print(myLower('AcdEjlG'))

def myUpper(src):
    src1 = ''
    for i in src:
        if 'a' <= i <= 'z':
            src1 += chr(ord(i) - 32)
        else:
            src1 += i
    return src1
#print(myUpper('aCdEf'))

第一种思路：
def myFind1(src,sub):
    for i in range(len(src)-len(sub)+1):
        new_src = src[i:i+len(sub)]
        #print(new_src)
        if new_src == sub:
            return i
    else:
        return -1
print(myFind1('abcde123abe','123a'))
第二种思路：
def myFind(src,sub):

    if len(sub) > len(src):
        return -1
    for i in range(len(src)):
        if src[i] == sub[0]:
            index = i
            for j in range(len(sub)):
                if src[index] != sub[j]:
                    break
                index += 1
            else:
                return i
    else:
        return -1

第一种思路：
def myRfind(src,sub):
    #从右往左进行遍历
    for i in range(len(src)-1,-1,-1):
        #先找第一个字符，如果一致，在进行对应切片比较
        if sub[0] == src[i]:
            #如果切片出来的结果与子串一致，返回所在的索引值
            if sub == src[i:i+len(sub)]:
                return i
    #如果没找到，返回-1
    else:
        return -1
# index = myRfind('abc123','c1')
# print(index)

第二种思路：
def myRfind(src,sub):
    if len(sub) > len(src):
        return -1
    for i in range(-1,-len(src)-1,-1):
        if src[i] == sub[0]:
            index = i
            for j in range(len(sub)):
                if src[index] != sub[j]:
                    break
                index += 1
            else:
                return len(src) + i
    else:
        return -1
#print(myRfind('abcdegabeda','ab'))

def myIsdigit(src):
    for ch in src:
        if not '0' <= ch <= '9':
            return False
    else:
        return True
print(myIsdigit('123'))
print(myIsdigit('123a'))

def myPartition(src,sub):
    if sub in src:
        #获取子串在目标字符串的索引值
        index = myRfind(src,sub)
        #切片操作划分三个元素：  1.str[0:index]  2.sub 3.[index+len(sub):]
        return (src[0:index],sub,src[index+len(sub):])
    else:
        return (src,'','')
# print(myPartition('abcdef','g'))
print(myPartition('abcdef','cd'))