Python 正则表达式用某些条件替换语法跳过行

Question

只有当行满足特定条件时，我才想在字符串中进行替换。

text_old = """
with some text 
some text as(
-- from text some text
with select text some other text
-- with text
from text
"""

我的替换在哪里 -

replacements = [
    ('with ','with \n'),
    ('as\n ','as'), 
    ('as\(','as (') 
        ]
for old, new in replacements:
    text_new = re.sub(old,new,text_old,flags=re.IGNORECASE)

如果该行以 -- 开头，我想跳过替换。所以 from 和 with 替换在这里被跳过 -

-- from text some text
-- with text

Answer 1

您可以使用 PyPi regex 模块使用纯正则表达式来解决这个问题。转到控制台/终端并运行pip install regex 命令。这将允许您在脚本中添加import regex，剩下要做的就是将(?<!^--.*) 添加到每个正则表达式中：

replacements = [
    (r'(?<!^--.*)\bwith ','with \n'),
    (r'(?<!^--.*)\bas\n ','as'), 
    (r'(?<!^--.*)\bas\(','as (') 
]

您还需要使用re.M (regex.M) 标志来确保^ 匹配所有行开始位置，而不仅仅是整个字符串的开始。 见Python demo：

import regex as re

text_old = """
with some text 
some text as(
-- from text some text
with select text some other text
-- with text
from text
"""

replacements = [
    (r'(?<!^--.*)\bwith ','with \n'),
    (r'(?<!^--.*)\bas\n ','as'), 
    (r'(?<!^--.*)\bas\(','as (') 
]
text_new = text_old
for old, new in replacements:
    text_new = re.sub(old,new,text_new,flags=re.I|re.M)

print(text_new)

输出：

with 
some text 
some text as (
-- from text some text
with 
select text some other text
-- with text
from text