关于python:python技巧替换文件中的某几行

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最近在写一个后端我的项目，次要的操作就是依据用户的前端数据，在后端关上我的项目中的代码文件，批改对应地位的参数，因为在目前的后端我的项目中常常应用这个操作，所以简略总结一下。

1. 文件门路：./test.c
2. 文件内容
……
case EPA:
      chan_desc->nb_taps        = 7;
      chan_desc->Td             = .410;
      chan_desc->channel_length = (int) (2*chan_desc->sampling_rate*chan_desc->Td + 1 + 2/(M_PI*M_PI)*log(4*M_PI*chan_desc->sampling_rate*chan_desc->Td));
      sum_amps = 0;
      chan_desc->amps           = (double *) malloc(chan_desc->nb_taps*sizeof(double));
      chan_desc->free_flags=chan_desc->free_flags|CHANMODEL_FREE_AMPS ;

      for (i = 0; i<chan_desc->nb_taps; i++) {chan_desc->amps[i]      = pow(10,.1*epa_amps_dB[i]);
        sum_amps += chan_desc->amps[i];
      }

      for (i = 0; i<chan_desc->nb_taps; i++)
        chan_desc->amps[i] /= sum_amps;

      chan_desc->delays         = epa_delays;
      chan_desc->ricean_factor  = 1;// 待批改地位
      chan_desc->aoa            = 0;// 待批改地位
      chan_desc->random_aoa     = 0;// 待批改地位
      chan_desc->ch             = (struct complexd **) malloc(nb_tx*nb_rx*sizeof(struct complexd *));
      chan_desc->chF            = (struct complexd **) malloc(nb_tx*nb_rx*sizeof(struct complexd *));
      chan_desc->a              = (struct complexd **) malloc(chan_desc->nb_taps*sizeof(struct complexd *));
……

读取文件
应用 python 中的 open()函数进行文件读取，将数据存储在缓冲区。
```
#1. 读取文件
path='./test.c'
with open(path, 'r') as file:
 file_content = file.read()
```

查找文件替换地位
以查找 chan_desc->ricean_factor = 1;// 待批改地位 为例，查找这句话的终点和起点。

## 注：此步骤须要 import re
#2. 查找文件替换地位
start_index=file_content.find('chan_desc->ricean_factor  =')# 终点
end_index=file_content.find('chan_desc->aoa            =',start_index)# 起点
if end_index==-1 or start_index==-1:
 print('未找到待批改地位')
#此时失去的两个指针，别离指向了待批改地位的终点和起点，如下图所示：

设置替换文件内容
假如目前只批改这一行的参数，

#3. 设置替换文件内容
ricean_factor=3# 假如这是要批改的参数信息
updata_content=file_content[:start_index]# 获取这行代码之前的内容
update_content+='chan_desc->ricean_factor  ='+str(ricean_factor)+';// 待批改地位'# 批改这行代码
update_content+=file_content[end_index:]# 获取这行代码之后的内容
#此时失去的 update_content 就是批改后的残缺文件内容，只批改了 ricean_factor 这一行的值

写入文件
同样应用 python 中的 open 函数。

#4. 写入文件
if update_content!="":# 如果批改内容不为空
 with open(path, 'w') as file:#w 示意笼罩写入，之前的内容都会被笼罩
     file.write(update_content)

总代码
整体的代码如下所示：

import re
#1. 读取文件
path='./test.c'
with open(path, 'r') as file:
 file_content = file.read()
#2. 查找文件替换地位
start_index=file_content.find('chan_desc->ricean_factor  =')# 终点
end_index=file_content.find('chan_desc->aoa            =',start_index)# 起点
if end_index==-1 or start_index==-1:
 print('未找到待批改地位')
#3. 设置替换文件内容
ricean_factor=3# 假如这是要批改的参数信息
updata_content=file_content[:start_index]# 获取这行代码之前的内容
update_content+='chan_desc->ricean_factor  ='+str(ricean_factor)+';// 待批改地位'# 批改这行代码
update_content+=file_content[end_index:]# 获取这行代码之后的内容
#4. 写入文件
if update_content!="":# 如果批改内容不为空
 with open(path, 'w') as file:#w 示意笼罩写入，之前的内容都会被笼罩
     file.write(update_content)

多行批改思路
多行批改有两种批改思路，如果批改局部比拟集中，则可间接替换一整块的字符串内容，如果批改局部较为扩散，则须要独自查找批改地位，而后再别离进行替换。

多行批改 - 整块替换

try:
 with open(file_path, "r") as file:
         file_content = file.read()
except Exception as e:
 return str(e)
# 设置改写内容
updated_content = ""
 # 查找批改
start_index_1 = file_content.find("start_sentence")# 要确保查找元素的唯一性
end_index_1 = file_content.find("end_sentence",start_index_1,) 

if start_index_1 == -1 or end_index_1 == -1:
 print("未找到待批改地位")
  return -1
 # 
 updated_content = file_content[:start_index_1]# 获取这行代码之前的内容
 updated_content += "start_sentence 和 end_sentence 之间的 sentence_1;\n"
 updated_content += "start_sentence 和 end_sentence 之间的 sentence_2;\n"
 updated_content +=file_content[end_index_1:]

 ## 此时 updated_content 就是批改后的残缺文件内容
 if updated_content != "":
  with open(file_path, "w") as file:
      file.write(updated_content)
else:
 print("批改失败")
 return -1

多行批改 - 部分替换

try:
 with open(file_path, "r") as file:
         file_content = file.read()
except Exception as e:
 return str(e)
# 设置改写内容
updated_content = ""
 # 查找批改
start_index_1 = file_content.find("start_sentence_1")# 要确保查找元素的唯一性
end_index_1 = file_content.find("end_sentence_1",start_index_1,) 
start_index_2 = file_content.find("start_sentence_2",end_index_1)
end_index_2 = file_content.find("end_sentence_2",start_index_2,)
start_index_3 = file_content.find("start_sentence_3",end_index_2)
end_index_3 = file_content.find("end_sentence_3",start_index_3,)
start_index_4 = file_content.find("start_sentence_4",end_index_3)
end_index_4 = file_content.find("end_sentence_4",start_index_4,)

if (
  start_index_1 == -1
  or end_index_1 == -1
  or start_index_2 == -1
  or end_index_2 == -1
  or start_index_3 == -1
  or end_index_3 == -1
  or start_index_4 == -1
  or end_index_4 == -1
 ):
 print("未找到待批改地位")
  return -1

 # 
 updated_content = file_content[:start_index_1]# 获取这行代码之前的内容
 updated_content += "start_sentence_1 和 end_sentence_1 之间的内容"
 updated_content +=file_content[end_index_1:start_index_2]
 updated_content += "start_sentence_2 和 end_sentence_2 之间的内容"
 updated_content +=file_content[end_index_2:start_index_3]
 updated_content += "start_sentence_3 和 end_sentence_3 之间的内容"
 updated_content +=file_content[end_index_3:start_index_4]
 updated_content += "start_sentence_4 和 end_sentence_4 之间的内容"
 updated_content += file_content[end_index_4:]

 ## 此时 updated_content 就是批改后的残缺文件内容
 if updated_content != "":
  with open(file_path, "w") as file:
      file.write(updated_content)
else:
 print("批改失败")
 return -1

正文完