从一个文件写入另一个python
[英]Writing from one file to another python
问题描述
I am trying to take some information I got from a webpage and write one of the variables to a file however I am having no luck it is probably very easy but I'm lost. 
我试图获取从网页中获取的一些信息，并将其中一个变量写入文件，但是运气不好，这可能很容易，但我迷路了。 Here is an example of one of the rows there are 1253 rows. 这是其中一个行的示例，其中有1253行。
<div class='entry qual-5 used-demoman slot-head bestprice custom' data-price='3280000' data-name="Kill-a-Watt Allbrero" data-quality="5" data-australium="normal" data-class="demoman" data-particle_effect="56" data-paint="" data-slot="cosmetic" data-consignment="consignment">
I am after the field called data-name it is not at the same spot in each row. 我在名为data-name的字段之后，它不在每一行的同一位置。 I tried this but it did not work 我尝试了这个，但是没有用
mfile=open('itemlist.txt','r')
mfile2=open('output.txt','a')
for row in mfile:
if char =='data-name':
mfile2.write(char)
Edit 1: 编辑1：
I made an example file of 'hello hi peanut' if did: 如果这样做，我制作了一个“ hello hi花生”的示例文件：
for row in mfile:
print row.index('hello')
it would print 0 as expected however when I changed the hello to hi it didnt return 1 it returned nothing. 它会按预期打印0，但是当我将hello更改为hi时，它没有返回1，则什么也没有返回。
2 个解决方案
解决方案1
3 已采纳 2015-07-05 20:55:16
Let's try to find the value using common string manipulation methods: 让我们尝试使用常见的字符串操作方法查找值：
>>> line = '''<div class='entry qual-5 used-demoman slot-head bestprice custom' data-price='3280000' data-name="Kill-a-Watt Allbrero" data-quality="5" data-australium="normal" data-class="demoman" data-particle_effect="56" data-paint="" data-slot="cosmetic" data-consignment="consignment">'''
We can use str.index to find the position of a string within a string: 我们可以使用str.index查找字符串在字符串中的位置：
>>> line.index('data-name')
87
So now we know we need to start looking at index 87 for the attribute we are interested in: 因此，现在我们知道我们需要开始查看索引87 ，查找我们感兴趣的属性：
>>> line[87:]
'data-name="Kill-a-Watt Allbrero" data-quality="5" data-australium="normal" data-class="demoman" data-particle_effect="56" data-paint="" data-slot="cosmetic" data-consignment="consignment">'
Now, we need to remove the data-name=" part too: 现在，我们也需要删除data-name="部分：
>>> start = line.index('data-name') + len('data-name="')
>>> start
98
>>> line[start:]
'Kill-a-Watt Allbrero" data-quality="5" data-australium="normal" data-class="demoman" data-particle_effect="56" data-paint="" data-slot="cosmetic" data-consignment="consignment">'
Now, we just need to find the index of the closing quotation mark too, and then we can extract just the attribute value: 现在，我们也只需要找到右引号的索引，然后就可以只提取属性值：
>>> end = line.index('"', start)
>>> end
118
>>> line[start:end]
'Kill-a-Watt Allbrero'
And then we have our solution: 然后我们有解决方案：
start = line.index('data-name') + len('data-name="')
end = line.index('"', start)
print(line[start:end])
We can put that in the loop: 我们可以将其放入循环中：
with open('itemlist.txt','r') as mfile, open('output.txt','a') as mfile2w
for line in mfile:
start = line.index('data-name') + len('data-name="')
end = line.index('"', start)
mfile2.write(line[start:end])
mfile2.write('\n')
解决方案2
1 2015-07-05 20:54:11
You can also use beautifulsoup : 您也可以使用beautifulsoup ：
a.html : a.html ：
<html>
<head>
<title> Asdf </title>
</head>
<body>
<div class='entry qual-5 used-demoman slot-head bestprice custom' data-price='3280000' data-name="Kill-a-Watt Allbrero" data-quality="5" data-australium="normal" data-class="demoman" data-particle_effect="56" data-paint="" data-slot="cosmetic" data-consignment="consignment">
</body>
</html>
a.py : a.py ：
from bs4 import BeautifulSoup
with open('a.html') as f:
lines = f.readlines()
soup = BeautifulSoup(''.join(lines), 'html.parser')
result = soup.findAll('div')[0]['data-price']
print result
# prints 3280000
My opinion is, if your task is pretty easy as in your example, there is actually no need of using beautifulsoup . 我的观点是，如果您的任务很简单，例如您的示例，那么实际上就不需要使用beautifulsoup 。 However, if it is more complicated, or it will be more complicated. 但是，如果更复杂，否则会更复杂。 Consider giving it a try with beautifulsoup . 考虑尝试使用beautifulsoup 。
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