【python技巧】替換檔案中的某幾行

1. 背景描述

最近在寫一個後端專案，主要的操作就是根據使用者的前端資料，在後端開啟專案中的程式碼檔案，修改對應位置的引數，因為在目前的後端專案中經常使用這個操作，所以簡單總結一下。

1. 檔案路徑：./test.c
2. 檔案內容
……
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;//待修改位置
      chan_desc->aoa            = 0;//待修改位置
      chan_desc->random_aoa     = 0;//待修改位置
      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 *));
……

2. 單行修改-操作步驟

1. 讀取檔案
   使用python中的open()函數進行檔案讀取，將資料儲存在緩衝區。

#1. 讀取檔案
path='./test.c'
with open(path, 'r') as file:
    file_content = file.read()

2. 查詢檔案替換位置
   以查詢chan_desc->ricean_factor = 1;//待修改位置為例，查詢這句話的起點和終點。

## 注：此步驟需要import re
#2. 查詢檔案替換位置
start_index=file_content.find('chan_desc->ricean_factor  = ')#起點
end_index=file_content.find('chan_desc->aoa            = ',start_index)#終點
if end_index==-1 or start_index==-1:
    print('未找到待修改位置')
#此時得到的兩個指標，分別指向了待修改位置的起點和終點，如下圖所示：

3. 設定替換檔案內容
   假設目前只修改這一行的引數，

#3. 設定替換檔案內容
ricean_factor=3#假設這是要修改的引數資訊
updata_content=file_content[:start_index]#獲取這行程式碼之前的內容
update_content+='chan_desc->ricean_factor  = '+str(ricean_factor)+';//待修改位置'#修改這行程式碼
update_content+=file_content[end_index:]#獲取這行程式碼之後的內容
#此時得到的update_content就是修改後的完整檔案內容，只修改了ricean_factor這一行的值

4. 寫入檔案
   同樣使用python中的open函數。

#4. 寫入檔案
if update_content!="":#如果修改內容不為空
    with open(path, 'w') as file:#w表示覆蓋寫入，之前的內容都會被覆蓋
        file.write(update_content)

5. 總程式碼
   整體的程式碼如下所示：

import re
#1. 讀取檔案
path='./test.c'
with open(path, 'r') as file:
    file_content = file.read()
#2. 查詢檔案替換位置
start_index=file_content.find('chan_desc->ricean_factor  = ')#起點
end_index=file_content.find('chan_desc->aoa            = ',start_index)#終點
if end_index==-1 or start_index==-1:
    print('未找到待修改位置')
#3. 設定替換檔案內容
ricean_factor=3#假設這是要修改的引數資訊
updata_content=file_content[:start_index]#獲取這行程式碼之前的內容
update_content+='chan_desc->ricean_factor  = '+str(ricean_factor)+';//待修改位置'#修改這行程式碼
update_content+=file_content[end_index:]#獲取這行程式碼之後的內容
#4. 寫入檔案
if update_content!="":#如果修改內容不為空
    with open(path, 'w') as file:#w表示覆蓋寫入，之前的內容都會被覆蓋
        file.write(update_content)

3. 多行修改-操作步驟

1. 多行修改思路
   多行修改有兩種修改思路，如果修改部分比較集中，則可直接替換一整塊的字串內容，如果修改部分較為分散，則需要單獨查詢修改位置，然後再分別進行替換。
2. 多行修改-整塊替換

try:
    with open(file_path, "r") as file:
            file_content = file.read()
except Exception as e:
    return str(e)
# 設定改寫內容
updated_content = ""
 # 查詢修改
start_index_1 = file_content.find("start_sentence")#要確保查詢元素的唯一性
end_index_1 = file_content.find("end_sentence",start_index_1,) 

if start_index_1 == -1 or end_index_1 == -1:
    print("未找到待修改位置")
     return -1
 # 
 updated_content = file_content[:start_index_1]#獲取這行程式碼之前的內容
 updated_content += "start_sentence和end_sentence之間的sentence_1;\n"
 updated_content += "start_sentence和end_sentence之間的sentence_2;\n"
 updated_content +=file_content[end_index_1:]

 ##此時updated_content就是修改後的完整檔案內容
 if updated_content != "":
     with open(file_path, "w") as file:
         file.write(updated_content)
else:
    print("修改失敗")
    return -1

3. 多行修改-區域性替換

try:
    with open(file_path, "r") as file:
            file_content = file.read()
except Exception as e:
    return str(e)
# 設定改寫內容
updated_content = ""
 # 查詢修改
start_index_1 = file_content.find("start_sentence_1")#要確保查詢元素的唯一性
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("未找到待修改位置")
     return -1

 # 
 updated_content = file_content[:start_index_1]#獲取這行程式碼之前的內容
 updated_content += "start_sentence_1和end_sentence_1之間的內容"
 updated_content +=file_content[end_index_1:start_index_2]
 updated_content += "start_sentence_2和end_sentence_2之間的內容"
 updated_content +=file_content[end_index_2:start_index_3]
 updated_content += "start_sentence_3和end_sentence_3之間的內容"
 updated_content +=file_content[end_index_3:start_index_4]
 updated_content += "start_sentence_4和end_sentence_4之間的內容"
 updated_content += file_content[end_index_4:]

 ##此時updated_content就是修改後的完整檔案內容
 if updated_content != "":
     with open(file_path, "w") as file:
         file.write(updated_content)
else:
    print("修改失敗")
    return -1