I am trying to rip some text out
of a large number
of html documents (numbers in the hundreds
of thousands). The documents are really forms but they are prepared by a very large group
of different organizations so there is significant variation in how they create the document. For example, the documents are divided into chapters. I might want to extract the contents
of Chapter 5 from every document so I can analyze the content
of the chapter. Initially I thought this would be easy but it turns out that the authors might use a set
of non-nested tables throughout the document to hold the content so that Chapter n could be displayed using td tags inside a table. Or they might use other elements such as p tags H tags, div tags or any other block level element.
After trying repeatedly to use lxml to help me identify the beginning and end
of each chapter I have determined that it is a lot cleaner to use a regular expression because in every case, no matter what the enclosing html element is the chapter label is always in the form
of
>Chapter #
It is a little more complicated in that there might be some white space or non-breaking space represented in different ways ( or or just spaces). Nonetheless it was trivial to write a regular expression to identify the beginning
of each section. (The beginning
of one section is the end
of the previous section.)
But now I want to use lxml to get the text out. My thought is that I have really no choice but to walk along my string to find the close tag for the element that encloses the text I am using to find the relevant section.
That is here is one example where the element holding the Chapter name is a div
<div style="DISPLAY: block; MARGIN-LEFT: 0pt; TEXT-INDENT: 0pt; MARGIN-RIGHT: 0pt" align="left"><font style="DISPLAY: inline; FONT-WEIGHT: bold; FONT-SIZE: 10pt; FONT-FAMILY: Times New Roman">Chapter 1.   Our Beginnings.</font></div>
So I am imagining that I would begin at the location where I found the match for chapter 1 and set up a regular expressions to find the next
</div|</td|</p|</h1 . . .
So at this point I have identified the type
of element holding my chapter heading
I can use the same logic to find all
of the text that is within that element that is set up a regular expression to help me mark from
>Chapter 1.   Our Beginnings.<
So I have identified where my Chapter 1 begins
I can do the same for chapter 2 (which is where Chapter 1 ends)
Now I am imagining that I am going to snip the document beginning at the opening
of the element that I identified as the element the indicates where chapter 1 begins and ending just before the opening
of the element that I identified as the element that indicates where Chapter 2 begins. The string that I have identified will then be fed to lxml to use its power to get the content.
I am going to all
of this trouble because I have read over and over - never use a regular expression to extract content from html documents and I have not hit on a way to be as accurate with lxml to identify the starting and ending locations for the text I want to extract. For example, I can never be certain that the subtitle
of Chapter 1 is Our Beginnings it could be Our Red Canary. Let me say that I spent two solid days trying with lxml to be confident that I had the beginning and ending elements and I could only be accurate <60%
of the time but a very short regular expression has given me better than 95% success.
I have a tendency to make things more complicated than necessary so I am wondering if anyone has seen or solved a similar problems and if they had an approach (not the details mind you) that they would like to offer.
