""":mod:`pandas.io.html` is a module containing functionality for dealing with
HTML IO.
"""
import os
import re
import numbers
import collections
from distutils.version import LooseVersion
import numpy as np
from pandas.core.dtypes.common import is_list_like
from pandas.errors import EmptyDataError
from pandas.io.common import (_is_url, urlopen,
parse_url, _validate_header_arg)
from pandas.io.parsers import TextParser
from pandas.compat import (lrange, lmap, u, string_types, iteritems,
raise_with_traceback, binary_type)
from pandas import Series
from pandas.core.common import AbstractMethodError
from pandas.io.formats.printing import pprint_thing
_IMPORTS = False
_HAS_BS4 = False
_HAS_LXML = False
_HAS_HTML5LIB = False
def _importers():
# import things we need
# but make this done on a first use basis
global _IMPORTS
if _IMPORTS:
return
_IMPORTS = True
global _HAS_BS4, _HAS_LXML, _HAS_HTML5LIB
try:
import bs4 # noqa
_HAS_BS4 = True
except ImportError:
pass
try:
import lxml # noqa
_HAS_LXML = True
except ImportError:
pass
try:
import html5lib # noqa
_HAS_HTML5LIB = True
except ImportError:
pass
#############
# READ HTML #
#############
_RE_WHITESPACE = re.compile(r'[\r\n]+|\s{2,}')
#正则表达式，空白标示符号，换行或者两个空格
char_types = string_types + (binary_type,)
#转换字符串 python3中：string_types = str binary_type = bytes
def _remove_whitespace(s, regex=_RE_WHITESPACE):
"""Replace extra whitespace inside of a string with a single space.
#替换字符串中多余的空白字符为一个空白字符
Parameters
----------
s : str or unicode
The string from which to remove extra whitespace.
#目标字符串
regex : regex
The regular expression to use to remove extra whitespace.
#空白字符串正则表达式
Returns
-------
subd : str or unicode
`s` with all extra whitespace replaced with a single space.
#返回替换后的字符串
"""
return regex.sub(' ', s.strip())
def _get_skiprows(skiprows):
"""Get an iterator given an integer, slice or container.
#获得跳过的行
Parameters
----------
skiprows : int, slice, container
The iterator to use to skip rows; can also be a slice.
Raises
------
TypeError
* If `skiprows` is not a slice, integer, or Container
Returns
-------
it : iterable
A proper iterator to use to skip rows of a DataFrame.
#返回一个迭代器对象，用于跳过指定的行
"""
if isinstance(skiprows, slice):
return lrange(skiprows.start or 0, skiprows.stop, skiprows.step or 1)
elif isinstance(skiprows, numbers.Integral) or is_list_like(skiprows):
return skiprows
elif skiprows is None:
return 0
raise TypeError('%r is not a valid type for skipping rows' %
type(skiprows).__name__)
def _read(obj):
"""Try to read from a url, file or string.
#读取，url/文件流或字符串
Parameters
----------
obj : str, unicode, or file-like
Returns
-------
raw_text : str
#返回字符串
"""
if _is_url(obj):
with urlopen(obj) as url:
text = url.read()
elif hasattr(obj, 'read'):
text = obj.read()
elif isinstance(obj, char_types):
text = obj
try:
if os.path.isfile(text):
with open(text, 'rb') as f:
return f.read()
except (TypeError, ValueError):
pass
else:
raise TypeError("Cannot read object of type %r" % type(obj).__name__)
return text
class _HtmlFrameParser(object):
"""Base class for parsers that parse HTML into DataFrames.
#将html转换为DataFrame的基类
Parameters
----------
io : str or file-like
This can be either a string of raw HTML, a valid URL using the HTTP,
FTP, or FILE protocols or a file-like object.
#解析的文件对象流
match : str or regex
The text to match in the document.
#正则表达式
attrs : dict
List of HTML <table> element attributes to match.
#表格属性
Attributes
----------
io : str or file-like
raw HTML, URL, or file-like object
match : regex
The text to match in the raw HTML
attrs : dict-like
A dictionary of valid table attributes to use to search for table
elements.
Notes
-----
To subclass this class effectively you must override the following methods:
#继承该类，必须重写下列方法
* :func:`_build_doc`
* :func:`_text_getter`
* :func:`_parse_td`
* :func:`_parse_tables`
* :func:`_parse_tr`
* :func:`_parse_thead`
* :func:`_parse_tbody`
* :func:`_parse_tfoot`
See each method's respective documentation for details on their
functionality.
"""
def __init__(self, io, match, attrs, encoding):
self.io = io
self.match = match
self.attrs = attrs
self.encoding = encoding
def parse_tables(self):
tables = self._parse_tables(self._build_doc(), self.match, self.attrs)
return (self._build_table(table) for table in tables)
def _parse_raw_data(self, rows):
"""Parse the raw data into a list of lists.
#将原始数据转换为一列列表
Parameters
----------
rows : iterable of node-like
A list of row elements.
行列表
text_getter : callable
A callable that gets the text from an individual node. This must be
defined by subclasses.
从单个节点获取文本
column_finder : callable
A callable that takes a row node as input and returns a list of the
column node in that row. This must be defined by subclasses.
#将每一个行作为输入，返回一个列表包含所有的列节点。将一行数据转换为一个列表对应columns。
Returns
-------
data : list of list of strings
#返回值： data = [['1','a','b'],['2','c','d']] data[0]代表一行，data[0][0]代表该行第一列元素
"""
data = [[_remove_whitespace(self._text_getter(col)) for col in
self._parse_td(row)] for row in rows]
return data
def _text_getter(self, obj):
"""Return the text of an individual DOM node.
#返回单个dom节点对应的文本
Parameters
----------
obj : node-like
A DOM node.
Returns
-------
text : str or unicode
The text from an individual DOM node.
"""
raise AbstractMethodError(self)
def _parse_td(self, obj):
"""Return the td elements from a row element.
#从行对应中提取单元格对象
Parameters
----------
obj : node-like
Returns
-------
columns : list of node-like
These are the elements of each row, i.e., the columns.
#返回值：一节列对象
"""
raise AbstractMethodError(self)
def _parse_tables(self, doc, match, attrs):
"""Return all tables from the parsed DOM.
#返回所有的表格，从dom中
Parameters
----------
doc : tree-like
The DOM from which to parse the table element.
match : str or regular expression
The text to search for in the DOM tree.
attrs : dict
A dictionary of table attributes that can be used to disambiguate
mutliple tables on a page.
Raises
------
ValueError
* If `match` does not match any text in the document.
Returns
-------
tables : list of node-like
A list of <table> elements to be parsed into raw data.
#返回doc中的table对象
"""
raise AbstractMethodError(self)
def _parse_tr(self, table):
"""Return the list of row elements from the parsed table element.
#从table中提取行对象
Parameters
----------
table : node-like
A table element that contains row elements.
Returns
-------
rows : list of node-like
A list row elements of a table, usually <tr> or <th> elements.
#返回值：一般为tr或th对象
"""
raise AbstractMethodError(self)
def _parse_thead(self, table):
"""Return the header of a table.
#返回表头
Parameters
----------
table : node-like
A table element that contains row elements.
Returns
-------
thead : node-like
A <thead>...</thead> element.
"""
raise AbstractMethodError(self)
def _parse_tbody(self, table):
"""Return the body of the table.
#返回表内容
Parameters
----------
table : node-like
A table element that contains row elements.
Returns
-------
tbody : node-like
A <tbody>...</tbody> element.
"""
raise AbstractMethodError(self)
def _parse_tfoot(self, table):
"""Return the footer of the table if any.
#返回表格的尾部
Parameters
----------
table : node-like
A table element that contains row elements.
Returns
-------
tfoot : node-like
A <tfoot>...</tfoot> element.
"""
raise AbstractMethodError(self)
def _build_doc(self):
"""Return a tree-like object that can be used to iterate over the DOM.
#返回一个树状对象，可以迭代DOM
Returns
-------
obj : tree-like
"""
raise AbstractMethodError(self)
def _build_table(self, table):
#返回表头、表体和表尾
header = self._parse_raw_thead(table)
body = self._parse_raw_tbody(table)
footer = self._parse_raw_tfoot(table)
return header, body, footer
def _parse_raw_thead(self, table):
thead = self._parse_thead(table)
res = []
if thead:
trs = self._parse_tr(thead[0])
for tr in trs:
#lmap = map
cols = lmap(self._text_getter, self._parse_td(tr))
if any([col != '' for col in cols]):
res.append(cols)
return res
def _parse_raw_tfoot(self, table):
tfoot = self._parse_tfoot(table)
res = []
if tfoot:
#lmap = map（func,iter）:将func作用于iter对象，返回一个可迭代对象
res = lmap(self._text_getter, self._parse_td(tfoot[0]))
#np.squeeze()将长度为1的多维度去掉，如x=np.array([[[1]],[[2]],[[3]]]]) np.squeeze(x)=np.array(1,2,3)
#np.atleast_1d将np转换为至少1维,如x =np.array(1,2,3) np.atleast_1d(x)=np.array([1],[2],[3])
return np.atleast_1d(
np.array(res).squeeze()) if res and len(res) == 1 else res
def _parse_raw_tbody(self, table):
tbody = self._parse_tbody(table)
try:
res = self._parse_tr(tbody[0])
except IndexError:
res = self._parse_tr(table)
return self._parse_raw_data(res)
class _BeautifulSoupHtml5LibFrameParser(_HtmlFrameParser):
"""HTML to DataFrame parser that uses BeautifulSoup under the hood.
#使用BeautifulSoup转换html成表格，继承_HtmlFrameParser
See Also
--------
pandas.io.html._HtmlFrameParser
pandas.io.html._LxmlFrameParser
Notes
-----
Documentation strings for this class are in the base class
:class:`pandas.io.html._HtmlFrameParser`.
"""
def __init__(self, *args, **kwargs):
super(_BeautifulSoupHtml5LibFrameParser, self).__init__(*args,
**kwargs)
from bs4 import SoupStrainer
#封装了许多匹配元素的方法，
self._strainer = SoupStrainer('table')
def _text_getter(self, obj):
#重写方法，返回对象文本
return obj.text
def _parse_td(self, row):
#在行中查找所有的td,th标签
return row.find_all(('td', 'th'))
def _parse_tr(self, element):
#在对象中查找所有的行标签‘tr’
return element.find_all('tr')
def _parse_th(self, element):
#在对象中找到所有的‘th’
return element.find_all('th')
def _parse_thead(self, table):
return table.find_all('thead')
def _parse_tbody(self, table):
return table.find_all('tbody')
def _parse_tfoot(self, table):
return table.find_all('tfoot')
def _parse_tables(self, doc, match, attrs):
#self._strainer.name = 'table'
element_name = self._strainer.name
tables = doc.find_all(element_name, attrs=attrs)
if not tables:
raise ValueError('No tables found')
result = []
unique_tables = set()
for table in tables:
if (table not in unique_tables and
table.find(text=match) is not None):
result.append(table)
unique_tables.add(table)
if not result:
raise ValueError("No tables found matching pattern %r" %
match.pattern)
return result
def _setup_build_doc(self):
raw_text = _read(self.io)
if not raw_text:
raise ValueError('No text parsed from document: %s' % self.io)
return raw_text
def _build_doc(self):
from bs4 import BeautifulSoup
return BeautifulSoup(self._setup_build_doc(), features='html5lib',
from_encoding=self.encoding)
def _build_xpath_expr(attrs):
"""Build an xpath expression to simulate bs4's ability to pass in kwargs to
search for attributes when using the lxml parser.
#将属性值转换为xpath表达式
Parameters
----------
attrs : dict
A dict of HTML attributes. These are NOT checked for validity.
Returns
-------
expr : unicode
An XPath expression that checks for the given HTML attributes.
"""
# give class attribute as class_ because class is a python keyword
if 'class_' in attrs:
attrs['class'] = attrs.pop('class_')
s = [u("@%s=%r") % (k, v) for k, v in iteritems(attrs)]
return u('[%s]') % ' and '.join(s)
_re_namespace = {'re': 'http://exslt.org/regular-expressions'}
_valid_schemes = 'http', 'file', 'ftp'
class _LxmlFrameParser(_HtmlFrameParser):
"""HTML to DataFrame parser that uses lxml under the hood.
#用lxml解析
Warning
-------
This parser can only handle HTTP, FTP, and FILE urls.
See Also
--------
_HtmlFrameParser
_BeautifulSoupLxmlFrameParser
Notes
-----
Documentation strings for this class are in the base class
:class:`_HtmlFrameParser`.
"""
def __init__(self, *args, **kwargs):
super(_LxmlFrameParser, self).__init__(*args, **kwargs)
def _text_getter(self, obj):
return obj.text_content()
def _parse_td(self, row):
return row.xpath('.//td|.//th')
def _parse_tr(self, table):
expr = './/tr[normalize-space()]'
return table.xpath(expr)
def _parse_tables(self, doc, match, kwargs):
pattern = match.pattern
# 1. check all descendants for the given pattern and only search tables
# 2. go up the tree until we find a table
query = '//table//*[re:test(text(), %r)]/ancestor::table'
xpath_expr = u(query) % pattern
# if any table attributes were given build an xpath expression to
# search for them
if kwargs:
xpath_expr += _build_xpath_expr(kwargs)
tables = doc.xpath(xpath_expr, namespaces=_re_namespace)
if not tables:
raise ValueError("No tables found matching regex %r" % pattern)
return tables
def _build_doc(self):
"""
Raises
------
ValueError
* If a URL that lxml cannot parse is passed.
Exception
* Any other ``Exception`` thrown. For example, trying to parse a
URL that is syntactically correct on a machine with no internet
connection will fail.
See Also
--------
pandas.io.html._HtmlFrameParser._build_doc
"""
from lxml.html import parse, fromstring, HTMLParser
from lxml.etree import XMLSyntaxError
parser = HTMLParser(recover=False, encoding=self.encoding)
try:
# try to parse the input in the simplest way
r = parse(self.io, parser=parser)
try:
r = r.getroot()
except AttributeError:
pass
except (UnicodeDecodeError, IOError):
# if the input is a blob of html goop
if not _is_url(self.io):
r = fromstring(self.io, parser=parser)
try:
r = r.getroot()
except AttributeError:
pass
else:
# not a url
scheme = parse_url(self.io).scheme
if scheme not in _valid_schemes:
# lxml can't parse it
msg = ('%r is not a valid url scheme, valid schemes are '
'%s') % (scheme, _valid_schemes)
raise ValueError(msg)
else:
# something else happened: maybe a faulty connection
raise
else:
if not hasattr(r, 'text_content'):
raise XMLSyntaxError("no text parsed from document", 0, 0, 0)
return r
def _parse_tbody(self, table):
return table.xpath('.//tbody')
def _parse_thead(self, table):
return table.xpath('.//thead')
def _parse_tfoot(self, table):
return table.xpath('.//tfoot')
def _parse_raw_thead(self, table):
expr = './/thead'
thead = table.xpath(expr)
res = []
if thead:
trs = self._parse_tr(thead[0])
for tr in trs:
cols = [_remove_whitespace(x.text_content()) for x in
self._parse_td(tr)]
if any([col != '' for col in cols]):
res.append(cols)
return res
def _parse_raw_tfoot(self, table):
expr = './/tfoot//th|//tfoot//td'
return [_remove_whitespace(x.text_content()) for x in
table.xpath(expr)]
def _expand_elements(body):
#k扩充元素 body = [['1','a','a','a'],['2','b'],['3','c','c']],
#扩充之后：body=[['1', 'a', 'a', 'a'], ['2', 'b', '', ''], ['3', 'c', 'c', '']]
#按照最大的length扩充其他行
lens = Series(lmap(len, body))
lens_max = lens.max()
not_max = lens[lens != lens_max]
empty = ['']
for ind, length in iteritems(not_max):
body[ind] += empty * (lens_max - length)
def _data_to_frame(**kwargs):
#将数据转换为DataFrame
head, body, foot = kwargs.pop('data')
header = kwargs.pop('header')
kwargs['skiprows'] = _get_skiprows(kwargs['skiprows'])
if head:
rows = lrange(len(head))
body = head + body
if header is None: # special case when a table has <th> elements
header = 0 if rows == [0] else rows
if foot:
body += [foot]
# fill out elements of body that are "ragged"
_expand_elements(body)
tp = TextParser(body, header=header, **kwargs)
df = tp.read()
return df
_valid_parsers = {'lxml': _LxmlFrameParser, None: _LxmlFrameParser,
'html5lib': _BeautifulSoupHtml5LibFrameParser,
'bs4': _BeautifulSoupHtml5LibFrameParser}
def _parser_dispatch(flavor):
"""Choose the parser based on the input flavor.
#选择转换器
Parameters
----------
flavor : str
The type of parser to use. This must be a valid backend.
Returns
-------
cls : _HtmlFrameParser subclass
The parser class based on the requested input flavor.
Raises
------
ValueError
* If `flavor` is not a valid backend.
ImportError
* If you do not have the requested `flavor`
"""
valid_parsers = list(_valid_parsers.keys())
if flavor not in valid_parsers:
raise ValueError('%r is not a valid flavor, valid flavors are %s' %
(flavor, valid_parsers))
if flavor in ('bs4', 'html5lib'):
if not _HAS_HTML5LIB:
raise ImportError("html5lib not found, please install it")
if not _HAS_BS4:
raise ImportError(
"BeautifulSoup4 (bs4) not found, please install it")
import bs4
if bs4.__version__ == LooseVersion('4.2.0'):
raise ValueError("You're using a version"
" of BeautifulSoup4 (4.2.0) that has been"
" known to cause problems on certain"
" operating systems such as Debian. "
"Please install a version of"
" BeautifulSoup4 != 4.2.0, both earlier"
" and later releases will work.")
else:
if not _HAS_LXML:
raise ImportError("lxml not found, please install it")
return _valid_parsers[flavor]
def _print_as_set(s):
return '{%s}' % ', '.join([pprint_thing(el) for el in s])
def _validate_flavor(flavor):
if flavor is None:
flavor = 'lxml', 'bs4'
elif isinstance(flavor, string_types):
flavor = flavor,
elif isinstance(flavor, collections.Iterable):
if not all(isinstance(flav, string_types) for flav in flavor):
raise TypeError('Object of type %r is not an iterable of strings' %
type(flavor).__name__)
else:
fmt = '{0!r}' if isinstance(flavor, string_types) else '{0}'
fmt += ' is not a valid flavor'
raise ValueError(fmt.format(flavor))
flavor = tuple(flavor)
valid_flavors = set(_valid_parsers)
flavor_set = set(flavor)
if not flavor_set & valid_flavors:
raise ValueError('%s is not a valid set of flavors, valid flavors are '
'%s' % (_print_as_set(flavor_set),
_print_as_set(valid_flavors)))
return flavor
def _parse(flavor, io, match, attrs, encoding, **kwargs):
flavor = _validate_flavor(flavor)
compiled_match = re.compile(match) # you can pass a compiled regex here
# hack around python 3 deleting the exception variable
retained = None
for flav in flavor:
parser = _parser_dispatch(flav)
p = parser(io, compiled_match, attrs, encoding)
try:
tables = p.parse_tables()
except Exception as caught:
retained = caught
else:
break
else:
raise_with_traceback(retained)
ret = []
for table in tables:
try:
ret.append(_data_to_frame(data=table, **kwargs))
except EmptyDataError: # empty table
continue
return ret
def read_html(io, match='.+', flavor=None, header=None, index_col=None,
skiprows=None, attrs=None, parse_dates=False,
tupleize_cols=False, thousands=',', encoding=None,
decimal='.', converters=None, na_values=None,
keep_default_na=True):
r"""Read HTML tables into a ``list`` of ``DataFrame`` objects.
Parameters
----------
io : str or file-like
A URL, a file-like object, or a raw string containing HTML. Note that
lxml only accepts the http, ftp and file url protocols. If you have a
URL that starts with ``'https'`` you might try removing the ``'s'``.
match : str or compiled regular expression, optional
The set of tables containing text matching this regex or string will be
returned. Unless the HTML is extremely simple you will probably need to
pass a non-empty string here. Defaults to '.+' (match any non-empty
string). The default value will return all tables contained on a page.
This value is converted to a regular expression so that there is
consistent behavior between Beautiful Soup and lxml.
flavor : str or None, container of strings
The parsing engine to use. 'bs4' and 'html5lib' are synonymous with
each other, they are both there for backwards compatibility. The
default of ``None`` tries to use ``lxml`` to parse and if that fails it
falls back on ``bs4`` + ``html5lib``.
header : int or list-like or None, optional
The row (or list of rows for a :class:`~pandas.MultiIndex`) to use to
make the columns headers.
index_col : int or list-like or None, optional
The column (or list of columns) to use to create the index.
skiprows : int or list-like or slice or None, optional
0-based. Number of rows to skip after parsing the column integer. If a
sequence of integers or a slice is given, will skip the rows indexed by
that sequence. Note that a single element sequence means 'skip the nth
row' whereas an integer means 'skip n rows'.
attrs : dict or None, optional
This is a dictionary of attributes that you can pass to use to identify
the table in the HTML. These are not checked for validity before being
passed to lxml or Beautiful Soup. However, these attributes must be
valid HTML table attributes to work correctly. For example, ::
attrs = {'id': 'table'}
is a valid attribute dictionary because the 'id' HTML tag attribute is
a valid HTML attribute for *any* HTML tag as per `this document
<http://www.w3.org/TR/html-markup/global-attributes.html>`__. ::
attrs = {'asdf': 'table'}
is *not* a valid attribute dictionary because 'asdf' is not a valid
HTML attribute even if it is a valid XML attribute. Valid HTML 4.01
table attributes can be found `here
<http://www.w3.org/TR/REC-html40/struct/tables.html#h-11.2>`__. A
working draft of the HTML 5 spec can be found `here
<http://www.w3.org/TR/html-markup/table.html>`__. It contains the
latest information on table attributes for the modern web.
parse_dates : bool, optional
See :func:`~pandas.read_csv` for more details.
tupleize_cols : bool, optional
If ``False`` try to parse multiple header rows into a
:class:`~pandas.MultiIndex`, otherwise return raw tuples. Defaults to
``False``.
thousands : str, optional
Separator to use to parse thousands. Defaults to ``','``.
encoding : str or None, optional
The encoding used to decode the web page. Defaults to ``None``.``None``
preserves the previous encoding behavior, which depends on the
underlying parser library (e.g., the parser library will try to use
the encoding provided by the document).
decimal : str, default '.'
Character to recognize as decimal point (e.g. use ',' for European
data).
.. versionadded:: 0.19.0
converters : dict, default None
Dict of functions for converting values in certain columns. Keys can
either be integers or column labels, values are functions that take one
input argument, the cell (not column) content, and return the
transformed content.
.. versionadded:: 0.19.0
na_values : iterable, default None
Custom NA values
.. versionadded:: 0.19.0
keep_default_na : bool, default True
If na_values are specified and keep_default_na is False the default NaN
values are overridden, otherwise they're appended to
.. versionadded:: 0.19.0
Returns
-------
dfs : list of DataFrames
Notes
-----
Before using this function you should read the :ref:`gotchas about the
HTML parsing libraries <io.html.gotchas>`.
Expect to do some cleanup after you call this function. For example, you
might need to manually assign column names if the column names are
converted to NaN when you pass the `header=0` argument. We try to assume as
little as possible about the structure of the table and push the
idiosyncrasies of the HTML contained in the table to the user.
This function searches for ``<table>`` elements and only for ``<tr>``
and ``<th>`` rows and ``<td>`` elements within each ``<tr>`` or ``<th>``
element in the table. ``<td>`` stands for "table data".
Similar to :func:`~pandas.read_csv` the `header` argument is applied
**after** `skiprows` is applied.
This function will *always* return a list of :class:`DataFrame` *or*
it will fail, e.g., it will *not* return an empty list.
Examples
--------
See the :ref:`read_html documentation in the IO section of the docs
<io.read_html>` for some examples of reading in HTML tables.
See Also
--------
pandas.read_csv
"""
_importers()
# Type check here. We don't want to parse only to fail because of an
# invalid value of an integer skiprows.
if isinstance(skiprows, numbers.Integral) and skiprows < 0:
raise ValueError('cannot skip rows starting from the end of the '
'data (you passed a negative value)')
_validate_header_arg(header)
return _parse(flavor=flavor, io=io, match=match, header=header,
index_col=index_col, skiprows=skiprows,
parse_dates=parse_dates, tupleize_cols=tupleize_cols,
thousands=thousands, attrs=attrs, encoding=encoding,
decimal=decimal, converters=converters, na_values=na_values,
keep_default_na=keep_default_na)
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