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[英]Python - How to replace a string in a text file where value is not known?
[英]Using python how do I insert a string in select lines of a text file where the inserted string depends on the content of the line and a known mapping?
背景
我有一个文本文件(它是一个 DAT 文件),我想将其导入到按原样格式化的程序中,尽管插入了一些小的附加字符串来选择行。 该文件太大而无法手动进行细微更改。
任意选择行具有以下定义属性:
select_string_
开头,后跟一个可以使用正则表达式检测到的唯一字符串$_
。对于每个选择行,我想要插入的确切字符串取决于这些字符串成员中的哪一个出现在该行的末尾以及一个已知的映射。
(非选择行包含任意字符串;它们不会按照一些简单的顺序出现。顺便说一句,对于所有选择行,上述唯一字符串$_
后跟_blah_
,这是正则表达式可检测的)
所以我们有,从第 1 行开始,如下所示:
select_string_$__blah_string_A
non_select_arbitrary_string
non_select_arbitrary_string
non_select_arbitrary_string
select_string_$__blah_string_A
non_select_arbitrary_string
non_select_arbitrary_string
non_select_arbitrary_string
select_string_$__blah_string_B
select_string_$__blah_string_B
non_select_arbitrary_string
non_select_arbitrary_string
select_string_$__blah_string_C
non_select_arbitrary_string
non_select_arbitrary_string
select_string_$__blah_string_C
对于给定的选择行,我要插入的文本属于$_
,并且我希望插入的特定字符串反映以下简单(广泛定义的)双射函数f :
f = {(string_A, f (string_A)), (string_B, f (string_B)), (string_C, f (string_C)))
以下字典捕获了此映射:
{'string_A' : '*f*(string_A)', 'string_B' : '*f*(string_B)', 'string_C' : '*f*(string_C)'}
因此,以string_A
为例:所有以string_A
结尾的选择string_A
应该在$_
之后插入f(string)
。 因此,我希望包含string_A
所有选择行如下所示:
select_string_$_f(string_A)_blah_string_A
从这个任意示例中概括我的问题如下:
题
使用 python 3,如何生成以下文本?
select_string_$_f(string_A)_blah_string_A
non_select_arbitrary_string
non_select_arbitrary_string
non_select_arbitrary_string
select_string_$_f(string_A)_blah_string_A
non_select_arbitrary_string
non_select_arbitrary_string
non_select_arbitrary_string
select_string_$_f(string_B)_blah_string_B
select_string_$_f(string_B)_blah_string_B
non_select_arbitrary_string
non_select_arbitrary_string
select_string_$_f(string_C)_blah_string_C
non_select_arbitrary_string
non_select_arbitrary_string
select_string_$_f(string_C)_blah_string_C
更一般地说:使用 python 如何在文本文件的选择行中插入字符串,其中插入的字符串取决于行的内容和已知映射?
考虑到$_
是您希望更改的所有行中的一个明显指示符,我们可以检查$_
的存在,并进一步检查string_a, b or c
的存在。
string_a = 'string_A'
string_b = 'string_B'
string_c = 'string_C'
testcases = ['select_string_$__blah_string_A', 'select_string_$__blah_string_B', 'select_string_$__blah_string_C', 'non_select_arbitrary_string']
result = []
for test in testcases:
if '$_' not in test:
result.append(test)
continue
check = test.split('$_')
if string_a in check[1]:
result.append(f'$_({string_a})'.join(check))
elif string_b in check[1]:
result.append(f'$_({string_b})'.join(check))
elif string_c in check[1]:
result.append(f'$_({string_c})'.join(check))
print(result)
#['select_string_$_(string_A)_blah_string_A', 'select_string_$_(string_B)_blah_string_B', 'select_string_$_(string_C)_blah_string_C', 'non_select_arbitrary_string']
从这里您可以将result
写回文件。
import re
fin = open("input.txt", "r")
fout = open("output.txt", "w")
for line in fin:
line = re.sub(r'^(select_string_\$_)(.*?(string_A|string_B|string_C))$', r'\1f(\3)\2', line)
fout.write(line)
鉴于您的示例,这会产生:
select_string_$_f(string_A)_blah_string_A
non_select_arbitrary_string
non_select_arbitrary_string
non_select_arbitrary_string
select_string_$_f(string_A)_blah_string_A
non_select_arbitrary_string
non_select_arbitrary_string
non_select_arbitrary_string
select_string_$_f(string_B)_blah_string_B
select_string_$_f(string_B)_blah_string_B
non_select_arbitrary_string
non_select_arbitrary_string
select_string_$_f(string_C)_blah_string_C
non_select_arbitrary_string
non_select_arbitrary_string
select_string_$_f(string_C)_blah_string_C
正则表达式解释:
^ # beginning of line
(select_string_\$_) # group 1, literally "select_string_$_"
( # group 2
.*? # 0 or more any character
(string_A|string_B|string_C) # group 3 one of string_A or string_B or string_C
) # end group 3
$ # end of line
替代品:
\1 # content of group 1
f(\3) # f(, content of group 3, )
\2 # content of group 2
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