我是 Python 新手，遇到一个问题：如何在现有字符串中插入一些字段？
例如，假设我从任何包含以下内容的文件中读取了一行：
line = "Name Age Group Class Profession"
现在我必须在 Class 字段之前的同一行中再插入 3rd Field(Group) 3 次。这意味着输出行应该是：
output_line = "Name Age Group Group Group Group Class Profession"
我可以轻松检索第三个字段（使用split 方法），但请告诉我插入字符串的最简单方法？
【问题讨论】：
line='Name Age Group Class Profession'
arr = line.split()
for i in range(3):
arr.insert(2, arr[2])
print(' '.join(arr))
【讨论】：
有几种方法可以做到这一点：
一种方法是使用切片：
>>> a="line=Name Age Group Class Profession"
>>> b=a.split()
>>> b[2:2]=[b[2]]*3
>>> b
['line=Name', 'Age', 'Group', 'Group', 'Group', 'Group', 'Class', 'Profession']
>>> a=" ".join(b)
>>> a
'line=Name Age Group Group Group Group Class Profession'
另一个是使用正则表达式：
>>> import re
>>> a=re.sub(r"(\S+\s+\S+\s+)(\S+\s+)(.*)", r"\1\2\2\2\2\3", a)
>>> a
'line=Name Age Group Group Group Group Class Profession'
【讨论】：
一个经常困扰新 Python 程序员但其他发帖者没有明确指出的重要一点是 Python 中的字符串是不可变的——您不能永远就地修改它们。
在 Python 中处理字符串时，您需要重新训练自己，而不是思考“如何修改这个字符串？”相反，您在想“如何创建一个新字符串，其中包含我已经得到的一些片段？”
【讨论】：
"how can I create a new string that has some pieces from this one I've already gotten?" 好的，但是如何？
为了让未来的“新手”解决这个问题，我认为这个帖子适合快速回答。
就像bgporter 所说：Python 字符串是不可变的，因此，要修改字符串，您必须利用已有的部分。
在以下示例中，我将'Fu' 插入到'Kong Panda'，以创建'Kong Fu Panda'
>>> line = 'Kong Panda'
>>> index = line.find('Panda')
>>> output_line = line[:index] + 'Fu ' + line[index:]
>>> output_line
'Kong Fu Panda'
在上面的示例中，我使用索引值将字符串“切片”为 2 个子字符串： 1 包含插入索引之前的子字符串，另一个包含其余部分。 然后我只需在两者之间添加所需的字符串，瞧，我们在另一个字符串中插入了一个字符串。
Python's slice notation 有一个很好的答案来解释字符串切片的主题。
【讨论】：
find() 将返回第一次出现的起始索引，如果未找到搜索字符串，它将返回-1。因此，这不会推广到感兴趣的字符串（在本例中为 Panda）可能多次出现或根本不出现的情况。
我知道这是不恰当的，但恕我直言，简单的方法是：
def insert (source_str, insert_str, pos):
return source_str[:pos]+insert_str+source_str[pos:]
【讨论】：
我的 DNA 分配遇到了类似的问题，我使用 bgporter 的建议来回答它。这是我创建一个新字符串的函数...
def insert_sequence(str1, str2, int):
""" (str1, str2, int) -> str
Return the DNA sequence obtained by inserting the
second DNA sequence into the first DNA sequence
at the given index.
>>> insert_sequence('CCGG', 'AT', 2)
CCATGG
>>> insert_sequence('CCGG', 'AT', 3)
CCGATG
>>> insert_sequence('CCGG', 'AT', 4)
CCGGAT
>>> insert_sequence('CCGG', 'AT', 0)
ATCCGG
>>> insert_sequence('CCGGAATTGG', 'AT', 6)
CCGGAAATTTGG
"""
str1_split1 = str1[:int]
str1_split2 = str1[int:]
new_string = str1_split1 + str2 + str1_split2
return new_string
【讨论】：
int，因为它会影响内置方法。当您稍后尝试使用 int("5") 之类的内容时，这可能会导致较大的程序出现问题。
下面的函数将允许将一个字符串插入另一个字符串：
def str_insert(from_me, into_me, at):
"""
Inserts the string <from_me> into <into_me>
Input <at> must be an integer index of <into_me> or a substring of <into_me>
Inserts <from_me> AFTER <at>, not before <at>
Inputs <from_me> and <into_me> must have working __str__ methods defined.
This is satisfied if they already are strings.
If not already strings, <from_me>, <into_me> are converted into strings.
If you try to insert an empty string, that's fine, and the result
is no different from the original.
In order to insert 'from_me' after nothing (insert at the beginning of the string) use:
at = '' or at = 0
"""
try:
return str_insert_or_raise(from_me, into_me, at)
except ValueError as err:
serr = str(err)
if (str_insert_or_raise.__name__ in serr) and 'not found' in serr and '<at>' in serr:
# if can't find where to insert stuff, don't bother to insert it
# use str_insert_or_raise if you want an exception instead
return into_me
else:
raise err
##############################################################
def str_insert_or_raise(from_me, into_me, at):
"""
Inserts the string <from_me> into <into_me>
Inserts <from_me> AFTER <at>, not before <at>
Input <at> must be an integer index of <into_me> or a substring of <into_me>
If <at> is the string '15', that substring will be searched for,
'15' will not be interpreted as an index/subscript.
Inputs <from_me> and <into_me> must have working __str__ methods defined.
If not already strings, <from_me>, <into_me> are converted into strings.
If you try to insert something, but we cannot find the position where
you said to insert it, then an exception is thrown guaranteed to at least
contain the following three substrings:
str_insert_or_raise.__name__
'not found'
'<at>'
"""
try:
if isinstance(at, int):
return str_insert_by_int(from_me, into_me, at)
# Below, the calls to str() work fine if <at> and <from_me> are already strings
# it makes them strings if they are not already
return str_insert_by_str(str(from_me), str(into_me), str(at))
except ValueError as err:
serr = str(err)
if 'empty string' in serr:
return into_me # We allow insertion of the empty string
elif ("<at>" in serr) and 'not found' in serr:
msg_start = "In " + str_insert_or_raise.__name__ + ": "
msg = [msg_start, "\ninput ", "<at> string", " not found in ", "<into_me>",
"\ninput <", str(at) , "> not found in <", str(into_me), ">"]
msg = ''.join(msg)
raise ValueError(msg) from None
else:
raise err
#############################################################
def str_insert_by_str(from_me, into_me, at):
"""
Inserts the string <from_me> into <into_me>
puts 'from_me' AFTER 'at', not before 'at'
For example,
str_insert_or_raise(at = '2', from_me = '0', into_me = '123')
puts the zero after the 2, not before the 2
The call returns '1203' not '1023'
Throws exceptions if input arguments are not strings.
Also, if <from_me> is empty or <at> is not a substring of <into_me> then
an exception is raised.
For fewer exceptions, use <str_insert_or_raise> instead.
"""
try:
s = into_me.replace(at, at + from_me, 1)
except TypeError as terr: # inputs to replace are not strings
msg_list = ['Inputs to function ', str_insert_by_str.__name__, '() must be strings']
raise TypeError(''.join(msg_list)) from None
# At the end of call to replace(), the '1' indicates we will replace
# the leftmost occurrence of <at>, instead of every occurrence of <at>
if (s == into_me): # <at> string not found and/or <from_me> is the empty string
msg_start = "In " + str_insert_by_str.__name__ + ": "
if from_me == '':
msg = ''.join([msg_start, "attempted to insert an empty string"])
raise ValueError(msg) from None
raise ValueError(msg_start, "Input <at> string not found in <into_me>.",
"\nUnable to determine where you want the substring inserted.") from None
return s
##################################################
def str_insert_by_int(from_me, into_me, at):
"""
* Inserts the string <from_me> into <into_me> at integer index <at>
* throws exceptions if input arguments are not strings.
* Also, throws an exception if you try to insert the empty string
* If <at> is less than zero, <from_me> gets placed at the
beginning of <into_me>
* If <at> is greater than the largest index of <into_me>,
<from_me> gets placed after the end of <into_me>
For fewer exceptions, use <str_insert_or_raise> instead.
"""
at = into_me[:(at if at > 0 else 0)]
return str_insert_by_str(from_me, into_me, at)
下面的代码演示了如何调用前面给出的str_insert函数
def foo(*args):
return args
F = 'F. '
s = 'Using the string \'John \' to specify where to make the insertion'
result = str_insert(from_me = F, into_me ='John Kennedy', at ='John ')
print(foo('\n\n', s, '\n', result))
s = 'Using an int returned by find(\'Ken\') to specify where to make the insertion'
index = 'John Kennedy'.find('Ken') # returns the position of the first letter of 'Ken', not the last letter
result = str_insert(from_me = F, into_me ='John Kennedy', at = index)
print(foo('\n\n', s, '\n', result))
s = 'Using an int (5) to specify where to make the insertion.'
result = str_insert(from_me = F, into_me ='John Kennedy', at = 5)
print(foo('\n\n', s, '\n', result))
s = "Looking for an 'at' string which does not exist"
result = str_insert(from_me = F, into_me ='John Kennedy', at ='x')
print(foo('\n\n', s, '\n', result))
s = ''.join(["Looking for the empty string.",
"\nFind one immediately at the beginning of the string"])
result = str_insert(from_me = F, into_me ='John Kennedy', at = '')
print(foo('\n\n', s, '\n', result))
s = "Insert an empty string at index 3. No visible change"
result = str_insert(from_me = '', into_me = 'John Kennedy', at = 3)
print(foo('\n\n', s, '\n', result))
for index in [-5, -1, 0, 1, 997, 999]:
s = "index " + str(index)
result = str_insert(from_me = F, into_me = 'John Kennedy', at = index)
print(foo('\n\n', s, '\n', result))
以上函数都不会“就地”修改字符串。每个函数都返回字符串的修改副本，但原始字符串保持不变。
例如，
s = ''.join(["Below is what we get when we forget ",
"to overwrite the string with the value",
" returned by str_insert_or_raise:"])
examp_str = 'John Kennedy'
str_insert('John ', F, examp_str)
print(foo('\n\n', s, '\n', examp_str))
# examp_str is still 'John Kennedy' without the F
【讨论】：
Insert characters of string in other string al located positions的答案
str1 = "ibuprofen"
str2 = "MEDICAL"
final_string=""
Value = 2
list2=[]
result=[str1[i:i+Value] for i in range(0, len(str1), Value)]
count = 0
for letter in result:
if count < len(result)-1:
final_string = letter + str2[count]
list2.append(final_string)
elif ((len(result)-1)==count):
list2.append(letter + str2[count:len(str2)])
break
count += 1
print(''.join(list2))
【讨论】：