小白求助，在看《python3-cookbook》遇到的问题

from collections import deque

def search(lines, pattern, history=5):
    previous_lines = deque(maxlen=history)
    for line in lines:
        if pattern in line:
            yield line, precious_lines
        previous_lines.append(line)

# Example use on a file
if __name__ == '__main__':
    with open(r'../../somefile.txt') as f:
        for line, preclines in search(f, 'python', 5):
            for pline in prevlines:
                print(pline, end='')
                print(line, end='')
                print('-' * 20)

代码运行没报错，但是为什么没有 print 出东西？我调试了一下，好像是search函数里yield后面的变量没有返回给line和preclines迭代，搞不懂为什么，是我理解错了吗？

line

pline

3 条回复

chenstack

2019-08-08 14:50:23 +08:00

贴出的代码有两处拼写错误
precious_lines -> previous_lines
preclines ->prevlines

改完后运行是 ok 的

somefile.txt:
java
python3
rust
php
js
c++
c
go
python3.7
ruby

output:
java
python3
--------------------
php
python3.7
--------------------
js
python3.7
--------------------
c++
python3.7
--------------------
c
python3.7
--------------------
go
python3.7
--------------------

scp404

2019-08-08 15:43:25 +08:00

我的错...代码贴错了

直接 copy 书里的源码是这样的

```
from collections import deque

def search(lines, pattern, history=5):
previous_lines = deque(maxlen=history)
for line in lines:
if pattern in line:
yield line, previous_lines
previous_lines.append(line)

# Example use on a file
if __name__ == '__main__':
with open(r'../../cookbook/somefile.txt') as f:
for line, prevlines in search(f, 'python', 5):
for pline in prevlines:
print(pline, end='')
print(line, end='')
print('-' * 20)
```

没打印出东西

我是不是回复不了图片。。。

scp404

2019-08-08 16:36:08 +08:00

@chenstack 我的错...代码贴错了，之前运行的时候变量名是对的。不过我把 txt 的内容换成老哥你的，能出结果。谢谢老哥了。