在 python 中的特定字符串之后搜索文本文件中的字符串

Question

Suppose this is the text file which has 10 line content.

1 mpe:p01 
2 mpe:p02 
3 * xyz 3 
4 mpe:p04 
5 mpe:p05 
6 mpe:p06 
7 mpe:p07 
8 mpe:p08 
9 mpe:p09 
10 mpe:p100 

I need to search string "mpe:" after "xyz" string.

My piece of code is:

str1_name ="* xyz"  
str2_name = "mpe:" ` 

lines = [] 

with open("textfile.txt",'r') as f:
   for line in f:
       if str2_name in line:
           lines.append(line)  
        lines2=lines[0]  
    print(lines2)

it is giving me output:

1 mpe:p0

but I want the output:

4 mpe:p0

Answer 1

You need to check if you encountered string xyz first. If you did, then set a flag to true. Then continue reading file. If previous line read was xyz , the flag would have been set to True . Check if current line has mpe and append that line to lines . See if this code works.

str1_name ="* xyz"  
str2_name = "mpe:" 
prev_xyz = False

lines = [] 

with open("textfile.txt",'r') as f:
    for line in f:
       if str2_name in line and prev_xyz:
           lines.append(line.strip())  
           #lines2=lines[0] prev line will strip out \n
       if str1_name in line:
           prev_xyz = True
       else:
           prev_xyz = False
print(lines2)

Output:

['4 mpe:p04']

Answer 2

lines = []
line_after_str1=[]

str1_name ="* xyz"

str2_name = "mpe:" 

with open("textfile.txt",'r') as f:
    all_lines=f.readlines()
    for line in range(len(all_lines)):
        
        if str1_name in all_lines[line]:
            line_after_str1.append(all_lines[line+1].replace('\n',''))
        elif str2_name in all_lines[line]:
            lines.append(all_lines[line].replace('\n',''))
        

print(line_after_str1)

Output:

['4 mpe:p04']

Answer 3

Well, if you're sure mpe follows xyz , you could run something like:

str1_name ="* xyz"  

with open("textfile.txt",'r') as f:
    for line in f:
        while str1_name not in line:
            pass
        if str2_name in line:
            print(next(f))

If the searched string doesn't follow immediately:

str1_name ="* xyz"
str2_name = "mpe:"  

checkpoint = False

with open("textfile.txt",'r') as f:
    for line in f:
        if str1_name in line:
            checkpoint = True
        if checkpoint and str2_name in line:
            print(line)
            break