在python中等效于grep -B的代码是什么？

发布时间：2020-12-20 11:06:20 所属栏目：Python 来源：网络整理

导读：参见英文答案 cat,grep and cut – translated to python????????????????????????????????????5个如何使用python从文件中的匹配字符串之前打印n行？ man grep -B NUM,–before-context=NUM Print NUM lines of leading context before matching lines. Pla

参见英文答案 > cat,grep and cut – translated to python????????????????????????????????????5个
如何使用python从文件中的匹配字符串之前打印n行？

man grep

-B NUM,–before-context=NUM

Print NUM lines of leading context before matching lines. Places a
line containing a group separator (–) between contiguous groups of
matches. With the -o or –only-matching option,this has no effect and
a warning is given.

我有grep -A的代码：
def grepA(word,file,num=0):
    with open(file) as f:
        for line in f:
            if word in line:
                print(line + ''.join(islice(file,num)))
                print('---')

解决方法

您只需要保留N个最后一行的缓冲区(列表),然后在遇到匹配时打印它们.

context_lines = []
for line in f:
    context_lines.append(line)
    if len(context_lines) > 5:  # Too many lines?
        context_lines.pop(0)  # Pop the first one off.
    if word in line:
        # context_lines already includes the `line` we're looking at
        for ctx_line in context_lines:  
             print(ctx_line)

（编辑：李大同）

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