python - 将特定字符串放置在特定索引处

Question

我想将字符串放置在某个索引处。假设我们从一个空字符串 x="" 开始。然后我想将字母 a、e、i、o 和 u 放在索引 0、2、4、6、8 处，以便得到 x="a e i o u"。然后，也许我想在索引 1,3,5 处添加 z,y,x，以便得到 x=azeyixo u。我怎样才能做到这一点？

Answer 1

你可以制作一个字符串生成器。这是一个开始。

>>> class MutableString:
...     def __init__(self, s):
...         self._string = s
...         
...     def __setitem__(self, index, s):
...         if index < len(self._string):
...             self._string = self._string[:index] + s + \
...                                self._string[index+len(s):]
...         else:
...             self._string = self._string + ' ' * \
...                                (index -len(self._string)) + s
...         
...     def __str__(self):
...         return self._string
...              
>>> ms = MutableString("hello world!")
>>> print ms
hello world!
>>> ms[6] = "people"
>>> print ms
hello people
>>> ms = MutableString('')
>>> ms[0] = 'a'; ms[2] = 'e'; ms[4] = 'i'; ms[6] = 'o'; ms[8] = 'u'
>>> print ms
a e i o u
>>> ms[1] = 'z'; ms[3] = 'y'; ms[5] = 'x'
>>> print ms
azeyixo u

或者使用字符列表作为字符串数据的内部表示:

>>> class CharArrayString:
...     def __init__(self, s=''):
...         self._strdata = [ch for ch in s]
... 
...     def __setitem__(self, index, s):
...         s  = [ch for ch in s]
...         sd = self._strdata
...         if type(index) != slice:
...             if index < len(sd):
...                 sd = sd[:index] + s + sd[index + len(s):]
...             else:
...                 sd = sd + [' '] * (index - len(sd)) + s
...         else:
...             sd[index] = s
...             
...         self._strdata = sd
... 
...     def __getitem__(self, index):
...         return ''.join(self._strdata[index])
... 
...     def __str__(self):
...         return ''.join(self._strdata)
... 
...     def __repr__(self):
...         return "ca_str('" + str(self) + "')"
...         
...     def __add__(self, s):
...         if isinstance(s, (CharArrayString, str)):
...             return CharArrayString(self._strdata + [ch for ch in s])
...         else:
...             raise TypeError(f"Catenation operation (+) "
...                             f"expected another CharArrayString "
...                             f"or str, but got {type(s)}.")
...

此版本支持前面的用法示例，以及通过 + 进行切片和串联。它并不是字面上的字符数组字符串 - 更像是字符串列表对象。无论如何:

>>> cas = CharArrayString("Hello world!")
>>> cas[::2]
'Hlowrd'
>>> cas[::-1]
'!dlrow olleH'
>>> cas + " Additional text."
ca_str('Hello world! Additional text.')
>>> cas
ca_str('Hello world!')
>>> cas += "Modifying cas."
>>> cas
ca_str('Hello world!Modifying cas.')
>>> cas[3:8] = '12345'
>>> cas
ca_str('Hel12345rld!Modifying cas.')