20190112-自定义实现字符串的操作方法，如strip,upper,title,ljust,center,zfill,find,rfind等

1：自定义实现strip()
Python strip() 方法用于移除字符串头尾指定的字符（默认为空格或换行符）或字符序列
算法：strip()仅移除首尾的指定字符，不能移除中间的先从首部开始移除

def customerize_strip(s,value=' '):
    result =''
    front =0
    end = len(s)
    #step1:找到首部顺序开始一个非指定字符的index
    for i in range(len(s)):
        if s[i] == value:
            continue
        else:
            front =i
            break
    #step2:找到尾部倒序开始第一个非指定字符的index
    for j in range(len(s)-1,-1,-1):
        #range是一个开区间，所有第一个值为len(s)-1,第二个值写作-1,表示取到第0位
        if s[j]==value:
            continue
        else:
            end = j
            break
    for k in range(front,end+1):
        result+=s[k]
    return result
print(s)
print(customerize_strip(s))

2：自定义实现str.upper()
算法，需要考虑字符串中不仅包含字母，可能还有其他字符的情况

def customerize_upper(s):
    result=''
    import string
    for i in s:
        if i in string.ascii_lowercase:
            result+=chr(ord(i)-32)
        else:
            result+=i
    return result
print(customerize_upper(s))

3.自定义实现str.lower()
算法，需要考虑字符串中不仅包含字母，可能还有其他字符的情况

def customerize_lower(s):
    result=''
    import string
    for i in s:
        if i in string.ascii_uppercase:
            result+=chr(ord(i)+32)
        else:
            result+=i
    return result
print(customerize_lower(s))

4.自定义实现str.swapcase()
Python swapcase() 方法用于对字符串的大小写字母进行转换

def customerize_swapcase(s):
    result =''
    import string
    for i in s:
        if i in string.ascii_uppercase:
            result+=chr(ord(i)+32)
        elif i in string.ascii_lowercase:
            result+=chr(ord(i)-32)
        else:
            result+=i
    return result
print(customerize_swapcase(s))

5.自定义实现str. capitalize()
Python capitalize()将字符串的第一个字母变成大写,其他字母变小写

def customerize_capitalize(s):
    result =''
    import string
    for i in range(len(s)):
        if i==0 and s[i] in string.ascii_lowercase:
            result+=chr(ord(s[i])-32)
        elif s[i] in string.ascii_uppercase:
            result+=chr(ord(s[i])+32)
        else:
            result+=s[i]
    return result
print(customerize_capitalize(s))

6.自定义实现str.title()
Python title() 方法返回"标题化"的字符串,就是说所有单词都是以大写开始，其余字母均为小写

def customerize_title(s):
    result =[]
    s= s.split()
    import string
    for i in s:
        each =''
        for j in range(len(i)):
            if j==0 and i[j] in string.ascii_lowercase:
                each += chr(ord(i[j])-32)
            else:
                each += i[j]
        result.append(each)
    return ' '.join(result)
s1= 'I am a good girl ha ha'
print(customerize_title(s1))

7.自定义实现str.ljust(numbe)
Python ljust() 方法返回一个原字符串左对齐,并使用空格填充至指定长度的新字符串。如果指定的长度小于原字符串的长度则返回原字符串

def customerize_ljust(s,lenth,fillchar=' '):
    if lenth<=len(s):
        return s
    else:
        fill =''
        for i in range(lenth-len(s)):
            fill+=fillchar
        result =s+fill
        return result
print(customerize_ljust(s1,23,'*'))
print(len(s1))
print(len(customerize_ljust(s1,23,'*')))

8.自定义实现str.center(numbe)
center() 方法返回一个指定的宽度 width 居中的字符串，fillchar 为填充的字符，默认为空格。如果指定的长度小于原字符串的长度则返回原字符串。

def customerize_center(s,lenth,fillchar=' '):
    if len(s)>lenth:
        return s
    else:
        result=''
        front_period=int((lenth-len(s))/2)
        end_period = lenth-front_period-len(s)
        for i in range(lenth):
            if i<front_period:
                result+=fillchar
            elif i>=front_period and i<lenth-end_period:
                result+=s[i-front_period]
            else:
                result+=fillchar
        return result
s2='aaa'
print(s2)
print(customerize_center(s2,7,'*'))

8.自定义实现zfill
Python zfill() 方法返回指定长度的字符串，原字符串右对齐，前面填充0

def customerize_zfill(s,lenth):
    if len(s)>lenth:
        return s
    else:
        result=''
        for i in range(lenth):
            if i<lenth-len(s):
                result+=str(0)
            else:
                result+=s[i-(lenth-len(s))]
        return result
print(customerize_zfill(s2,10))

9.自定义find函数
Python find() 方法检测字符串中是否包含子字符串 str ，如果指定 beg（开始） 和 end（结束） 范围，则检查是否包含在指定范围内，如果包含子字符串返回开始的索引值，否则返回-1

def customerize_find(s,str,beg=None,end = None):
    if beg == None:
        beg = 0
    if end ==None:
        end = len(s)
    for i in range(beg,end):
        if s[i:i+len(str)]==str:
            return i
    else:
        return -1
s3='lkadsacedsfhlkwheldsfsdfskadsface'
print(s3)
print(customerize_find(s3,'ace'))
print(customerize_find(s3,'ace',9))

10.自定义实现rfind
Python rfind() 返回字符串最后一次出现的位置(从右向左查询)，如果没有匹配项则返回-1

def customerize_rfind(s,str,beg=None,end=None):
    if beg == None:
        beg = 0
    if end ==None:
        end = len(s)
    for i in range(end,beg-1,-1):
        if s[i-len(str):i]==str:
            if i-len(str)>=beg:
                return i-len(str)
    else:
        return -1
print(s3)
print(customerize_rfind(s3,'ace'))
print(customerize_rfind(s3,'ace',3,8))