Python使用PDFMiner解析PDF

  近期在做爬虫时有时会遇到网站只提供pdf的情况,这样就不能使用scrapy直接抓取页面内容了,只能通过解析PDF的方式处理,目前的解决方案大致只有pyPDFPDFMiner。因为据说PDFMiner更适合文本的解析,而我需要解析的正是文本,因此最后选择使用PDFMiner(这也就意味着我对pyPDF一无所知了)

  首先说明的是解析PDF是非常蛋疼的事,即使是PDFMiner对于格式不工整的PDF解析效果也不怎么样,所以连PDFMiner的开发者都吐槽PDF is evil. 不过这些并不重要。官方文档在此:http://www.unixuser.org/~euske/python/pdfminer/index.html

  一.安装:

  1.首先下载源文件包 http://pypi.python.org/pypi/pdfminer/,解压,然后命令行安装即可:python setup.py install

  2.安装完成后使用该命令行测试:pdf2txt.py samples/simple1.pdf如果显示以下内容则表示安装成功:

Hello World Hello World H e l l o W o r l d H e l l o W o r l d

     3.如果要使用中日韩文字则需要先编译再安装: 

# make cmap

python tools/conv_cmap.py pdfminer/cmap Adobe-CNS1 cmaprsrc/cid2code_Adobe_CNS1.txtreading 'cmaprsrc/cid2code_Adobe_CNS1.txt'...writing 'CNS1_H.py'......(this may take several minutes) 

# python setup.py install  

 二.使用

 由于解析PDF是一件非常耗时和内存的工作,因此PDFMiner使用了一种称作lazy parsing的策略,只在需要的时候才去解析,以减少时间和内存的使用。要解析PDF至少需要两个类:PDFParser 和 PDFDocument,PDFParser 从文件中提取数据,PDFDocument保存数据。另外还需要PDFPageInterpreter去处理页面内容,PDFDevice将其转换为我们所需要的。PDFResourceManager用于保存共享内容例如字体或图片。

 

Figure 1. Relationships between PDFMiner classes

  

比较重要的是Layout,主要包括以下这些组件:

LTPage

Represents an entire page. May contain child objects like LTTextBox, LTFigure, LTImage, LTRect, LTCurve and LTLine.

LTTextBox

Represents a group of text chunks that can be contained in a rectangular area. Note that this box is created by geometric analysis and does not necessarily represents a logical boundary of the text. It contains a list of LTTextLine objects. get_text() method returns the text content.

LTTextLine

Contains a list of LTChar objects that represent a single text line. The characters are aligned either horizontaly or vertically, depending on the text's writing mode. get_text() method returns the text content.

LTChar

LTAnno

Represent an actual letter in the text as a Unicode string. Note that, while a LTChar object has actual boundaries, LTAnno objects does not, as these are "virtual" characters, inserted by a layout analyzer according to the relationship between two characters (e.g. a space).

LTFigure

Represents an area used by PDF Form objects. PDF Forms can be used to present figures or pictures by embedding yet another PDF document within a page. Note that LTFigure objects can appear recursively.

LTImage

Represents an image object. Embedded images can be in JPEG or other formats, but currently PDFMiner does not pay much attention to graphical objects.

LTLine

Represents a single straight line. Could be used for separating text or figures.

LTRect

Represents a rectangle. Could be used for framing another pictures or figures.

LTCurve

Represents a generic Bezier curve.

 

 

 

             Figure 2. Layout objects and its tree structure

 

官方文档给了几个Demo但是都过于简略,虽然给了一个详细一些的Demo,但链接地址是旧的现在已经失效,不过最终还是找到了新的地址:http://denis.papathanasiou.org/posts/2010.08.04.post.html

这个Demo就比较详细了,源码如下:

 

  1 #!/usr/bin/python
  2 
  3 import sys
  4 import os
  5 from binascii import b2a_hex
  6 
  7 
  8 ###
  9 ### pdf-miner requirements
 10 ###
 11 
 12 from pdfminer.pdfparser import PDFParser
 13 from pdfminer.pdfdocument import PDFDocument, PDFNoOutlines
 14 from pdfminer.pdfpage import PDFPage
 15 from pdfminer.pdfinterp import PDFResourceManager, PDFPageInterpreter
 16 from pdfminer.converter import PDFPageAggregator
 17 from pdfminer.layout import LAParams, LTTextBox, LTTextLine, LTFigure, LTImage, LTChar
 18 
 19 def with_pdf (pdf_doc, fn, pdf_pwd, *args):
 20     """Open the pdf document, and apply the function, returning the results"""
 21     result = None
 22     try:
 23         # open the pdf file
 24         fp = open(pdf_doc, 'rb')
 25         # create a parser object associated with the file object
 26         parser = PDFParser(fp)
 27         # create a PDFDocument object that stores the document structure
 28         doc = PDFDocument(parser, pdf_pwd)
 29         # connect the parser and document objects
 30         parser.set_document(doc)
 31         # supply the password for initialization
 32 
 33         if doc.is_extractable:
 34             # apply the function and return the result
 35             result = fn(doc, *args)
 36 
 37         # close the pdf file
 38         fp.close()
 39     except IOError:
 40         # the file doesn't exist or similar problem
 41         pass
 42     return result
 43 
 44 
 45 ### 
 46 ### Table of Contents
 47 ### 
 48 
 49 def _parse_toc (doc):
 50     """With an open PDFDocument object, get the table of contents (toc) data
 51     [this is a higher-order function to be passed to with_pdf()]"""
 52     toc = []
 53     try:
 54         outlines = doc.get_outlines()
 55         for (level,title,dest,a,se) in outlines:
 56             toc.append( (level, title) )
 57     except PDFNoOutlines:
 58         pass
 59     return toc
 60 
 61 def get_toc (pdf_doc, pdf_pwd=''):
 62     """Return the table of contents (toc), if any, for this pdf file"""
 63     return with_pdf(pdf_doc, _parse_toc, pdf_pwd)
 64 
 65 
 66 ###
 67 ### Extracting Images
 68 ###
 69 
 70 def write_file (folder, filename, filedata, flags='w'):
 71     """Write the file data to the folder and filename combination
 72     (flags: 'w' for write text, 'wb' for write binary, use 'a' instead of 'w' for append)"""
 73     result = False
 74     if os.path.isdir(folder):
 75         try:
 76             file_obj = open(os.path.join(folder, filename), flags)
 77             file_obj.write(filedata)
 78             file_obj.close()
 79             result = True
 80         except IOError:
 81             pass
 82     return result
 83 
 84 def determine_image_type (stream_first_4_bytes):
 85     """Find out the image file type based on the magic number comparison of the first 4 (or 2) bytes"""
 86     file_type = None
 87     bytes_as_hex = b2a_hex(stream_first_4_bytes)
 88     if bytes_as_hex.startswith('ffd8'):
 89         file_type = '.jpeg'
 90     elif bytes_as_hex == '89504e47':
 91         file_type = '.png'
 92     elif bytes_as_hex == '47494638':
 93         file_type = '.gif'
 94     elif bytes_as_hex.startswith('424d'):
 95         file_type = '.bmp'
 96     return file_type
 97 
 98 def save_image (lt_image, page_number, images_folder):
 99     """Try to save the image data from this LTImage object, and return the file name, if successful"""
100     result = None
101     if lt_image.stream:
102         file_stream = lt_image.stream.get_rawdata()
103         if file_stream:
104             file_ext = determine_image_type(file_stream[0:4])
105             if file_ext:
106                 file_name = ''.join([str(page_number), '_', lt_image.name, file_ext])
107                 if write_file(images_folder, file_name, file_stream, flags='wb'):
108                     result = file_name
109     return result
110 
111 
112 ###
113 ### Extracting Text
114 ###
115 
116 def to_bytestring (s, enc='utf-8'):
117     """Convert the given unicode string to a bytestring, using the standard encoding,
118     unless it's already a bytestring"""
119     if s:
120         if isinstance(s, str):
121             return s
122         else:
123             return s.encode(enc)
124 
125 def update_page_text_hash (h, lt_obj, pct=0.2):
126     """Use the bbox x0,x1 values within pct% to produce lists of associated text within the hash"""
127 
128     x0 = lt_obj.bbox[0]
129     x1 = lt_obj.bbox[2]
130 
131     key_found = False
132     for k, v in h.items():
133         hash_x0 = k[0]
134         if x0 >= (hash_x0 * (1.0-pct)) and (hash_x0 * (1.0+pct)) >= x0:
135             hash_x1 = k[1]
136             if x1 >= (hash_x1 * (1.0-pct)) and (hash_x1 * (1.0+pct)) >= x1:
137                 # the text inside this LT* object was positioned at the same
138                 # width as a prior series of text, so it belongs together
139                 key_found = True
140                 v.append(to_bytestring(lt_obj.get_text()))
141                 h[k] = v
142     if not key_found:
143         # the text, based on width, is a new series,
144         # so it gets its own series (entry in the hash)
145         h[(x0,x1)] = [to_bytestring(lt_obj.get_text())]
146 
147     return h
148 
149 def parse_lt_objs (lt_objs, page_number, images_folder, text=[]):
150     """Iterate through the list of LT* objects and capture the text or image data contained in each"""
151     text_content = [] 
152 
153     page_text = {} # k=(x0, x1) of the bbox, v=list of text strings within that bbox width (physical column)
154     for lt_obj in lt_objs:
155         if isinstance(lt_obj, LTTextBox) or isinstance(lt_obj, LTTextLine):
156             # text, so arrange is logically based on its column width
157             page_text = update_page_text_hash(page_text, lt_obj)
158         elif isinstance(lt_obj, LTImage):
159             # an image, so save it to the designated folder, and note its place in the text 
160             saved_file = save_image(lt_obj, page_number, images_folder)
161             if saved_file:
162                 # use html style <img /> tag to mark the position of the image within the text
163                 text_content.append('<img src="'+os.path.join(images_folder, saved_file)+'" />')
164             else:
165                 print >> sys.stderr, "error saving image on page", page_number, lt_obj.__repr__
166         elif isinstance(lt_obj, LTFigure):
167             # LTFigure objects are containers for other LT* objects, so recurse through the children
168             text_content.append(parse_lt_objs(lt_obj, page_number, images_folder, text_content))
169 
170     for k, v in sorted([(key,value) for (key,value) in page_text.items()]):
171         # sort the page_text hash by the keys (x0,x1 values of the bbox),
172         # which produces a top-down, left-to-right sequence of related columns
173         text_content.append(''.join(v))
174 
175     return '\n'.join(text_content)
176 
177 
178 ###
179 ### Processing Pages
180 ###
181 
182 def _parse_pages (doc, images_folder):
183     """With an open PDFDocument object, get the pages and parse each one
184     [this is a higher-order function to be passed to with_pdf()]"""
185     rsrcmgr = PDFResourceManager()
186     laparams = LAParams()
187     device = PDFPageAggregator(rsrcmgr, laparams=laparams)
188     interpreter = PDFPageInterpreter(rsrcmgr, device)
189 
190     text_content = []
191     for i, page in enumerate(PDFPage.create_pages(doc)):
192         interpreter.process_page(page)
193         # receive the LTPage object for this page
194         layout = device.get_result()
195         # layout is an LTPage object which may contain child objects like LTTextBox, LTFigure, LTImage, etc.
196         text_content.append(parse_lt_objs(layout, (i+1), images_folder))
197 
198     return text_content
199 
200 def get_pages (pdf_doc, pdf_pwd='', images_folder='/tmp'):
201     """Process each of the pages in this pdf file and return a list of strings representing the text found in each page"""
202     return with_pdf(pdf_doc, _parse_pages, pdf_pwd, *tuple([images_folder]))
203 
204 a = open('a.txt','a')
205 for i in get_pages('/home/jamespei/nova.pdf'):
206     a.write(i)
207 a.close()

 

这段代码重点在于第128行,可以看到PDFMiner是一种基于坐标来解析的框架,PDF中能解析的组件全都包括上下左右边缘的坐标,如x0 = lt_obj.bbox[0]就是lt_obj元素的左边缘的坐标,同理x1则为右边缘。以上代码的意思就是把所有x0且x1的坐标相差在20%以内的元素分成一组,这样就实现了从PDF文件中定向抽取内容。

---------------------------补充-------------------------

有一个需要注意的地方,在解析有些PDF的时候会报这样的异常:pdfminer.pdfdocument.PDFEncryptionError: Unknown algorithm: param={'CF': {'StdCF': {'Length': 16, 'CFM': /AESV2, 'AuthEvent': /DocOpen}}, 'O': '\xe4\xe74\xb86/\xa8)\xa6x\xe6\xa3/U\xdf\x0fWR\x9cPh\xac\xae\x88B\x06_\xb0\x93@\x9f\x8d', 'Filter': /Standard, 'P': -1340, 'Length': 128, 'R': 4, 'U': '|UTX#f\xc9V\x18\x87z\x10\xcb\xf5{\xa7\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00', 'V': 4, 'StmF': /StdCF, 'StrF': /StdCF}

从字面意思来看是因为这个PDF是一个加密的PDF,所以无法解析 ,但是如果直接打开PDF却是可以的并没有要求输密码什么的,原因是这个PDF虽然是加过密的,但密码是空,所以就出现了这样的问题。

解决这个的问题的办法是通过qpdf命令来解密文件(要确保已经安装了qpdf),要想在python中调用该命令只需使用call即可:

1 from subprocess import call
2 call('qpdf --password=%s --decrypt %s %s' %('', file_path, new_file_path), shell=True)

其中参数file_path是要解密的PDF的路径,new_file_path是解密后的PDF文件路径,然后使用解密后的文件去做解析就OK了

posted @ 2016-04-05 17:14 JamesPei 阅读(...) 评论(...) 编辑 收藏