Python实现：仅打印后续紧跟'y行'的目标'x行'

输入文件内容 #

this is line x  
this is line y  
this is line x 
this is line x  
this is line x  
this is line y   
this is line x  
this is line x  
this is line y

需求说明 #

仅当this is line y出现在this is line x之后时，打印该this is line x（本示例应仅打印3次）。

尝试的代码（不符合需求） #

skip_line = True  
with open("input_n.txt","r") as myfile:
     for line in myfile:
        if "x" in line:
            skip_line = False
        elif "y" in line:
            skip_line = True
        else:
            pass
        if skip_line:
            continue
        print(line)

这段代码会打印所有this is line x，无法满足“仅打印后面跟着'y'的'x'行”的要求。

修改后的代码方案 #

核心思路是检查每一行的下一行是否为'y'行，只有当前行是'x'且下一行是'y'时，才打印当前行：

with open("input_n.txt", "r") as myfile:
    # 读取所有行并去除换行符，方便后续处理
    lines = [line.rstrip('\n') for line in myfile]

# 遍历到倒数第二行，避免索引越界
for i in range(len(lines) - 1):
    current_line = lines[i]
    next_line = lines[i + 1]
    if "x" in current_line and "y" in next_line:
        print(current_line)

代码说明 #

1. 先把文件所有行加载到列表中，这样可以方便地访问当前行的下一行内容。
2. 遍历列表时只到倒数第二行，防止访问lines[i+1]时出现索引越界错误。
3. 仅当当前行包含'x'且下一行包含'y'时，才打印当前的'x'行，正好匹配需求中的3次打印结果。

内容的提问来源于stack exchange，提问作者Kish Kharka