Python爬虫入门
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网络爬虫(又被称为网页蜘蛛,网络机器人,在FOAF社区中间,更经常的称为网页追逐者),是一种按照一定的规则,自动的抓取万维网信息的程序或者脚本。
一、urllib简介
python3中的urllib模块相对于Python2做了很大的改变,原来的urllib、urllib2、urlparse和robotparse模块被去掉了,新的urllib模块分为5个子模块,改变日志文件内容如下:
a new urllib package was created. It consists of code from urllib, urllib2, urlparse, and robotparser. The old modules have all been removed. The new package has five submodules: urllib.parse, urllib.request, urllib.response, urllib.error, and urllib.robotparser. The urllib.request.urlopen() function uses the url opener from urllib2. (Note that the unittests have not been renamed for the beta, but they will be renamed in the future.)
使用help()可以查看Python3中的urllib模块:
>>> import urllib >>> help(urllib) Help on package urllib: NAME urllib MODULE REFERENCE http://docs.python.org/3.5/library/urllib The following documentation is automatically generated from the Python source files. It may be incomplete, incorrect or include features that are considered implementation detail and may vary between Python implementations. When in doubt, consult the module reference at the location listed above. PACKAGE CONTENTS error parse request response robotparser FILE /usr/local/python35/lib/python3.5/urllib/__init__.py
"""Exception classes raised by urllib. The base exception class is URLError, which inherits from OSError. It doesn‘t define any behavior of its own, but is the base class for all exceptions defined in this package. HTTPError is an exception class that is also a valid HTTP response instance. It behaves this way because HTTP protocol errors are valid responses, with a status code, headers, and a body. In some contexts, an application may want to handle an exception like a regular response. """ import urllib.response __all__ = [‘URLError‘, ‘HTTPError‘, ‘ContentTooShortError‘] # do these error classes make sense? # make sure all of the OSError stuff is overridden. we just want to be # subtypes. class URLError(OSError): # URLError is a sub-type of OSError, but it doesn‘t share any of # the implementation. need to override __init__ and __str__. # It sets self.args for compatibility with other EnvironmentError # subclasses, but args doesn‘t have the typical format with errno in # slot 0 and strerror in slot 1. This may be better than nothing. def __init__(self, reason, filename=None): self.args = reason, self.reason = reason if filename is not None: self.filename = filename def __str__(self): return ‘<urlopen error %s>‘ % self.reason class HTTPError(URLError, urllib.response.addinfourl): """Raised when HTTP error occurs, but also acts like non-error return""" __super_init = urllib.response.addinfourl.__init__ def __init__(self, url, code, msg, hdrs, fp): self.code = code self.msg = msg self.hdrs = hdrs self.fp = fp self.filename = url # The addinfourl classes depend on fp being a valid file # object. In some cases, the HTTPError may not have a valid # file object. If this happens, the simplest workaround is to # not initialize the base classes. if fp is not None: self.__super_init(fp, hdrs, url, code) def __str__(self): return ‘HTTP Error %s: %s‘ % (self.code, self.msg) def __repr__(self): return ‘<HTTPError %s: %r>‘ % (self.code, self.msg) # since URLError specifies a .reason attribute, HTTPError should also # provide this attribute. See issue13211 for discussion. @property def reason(self): return self.msg @property def headers(self): return self.hdrs @headers.setter def headers(self, headers): self.hdrs = headers class ContentTooShortError(URLError): """Exception raised when downloaded size does not match content-length.""" def __init__(self, message, content): URLError.__init__(self, message) self.content = content
"""Parse (absolute and relative) URLs. urlparse module is based upon the following RFC specifications. RFC 3986 (STD66): "Uniform Resource Identifiers" by T. Berners-Lee, R. Fielding and L. Masinter, January 2005. RFC 2732 : "Format for Literal IPv6 Addresses in URL‘s by R.Hinden, B.Carpenter and L.Masinter, December 1999. RFC 2396: "Uniform Resource Identifiers (URI)": Generic Syntax by T. Berners-Lee, R. Fielding, and L. Masinter, August 1998. RFC 2368: "The mailto URL scheme", by P.Hoffman , L Masinter, J. Zawinski, July 1998. RFC 1808: "Relative Uniform Resource Locators", by R. Fielding, UC Irvine, June 1995. RFC 1738: "Uniform Resource Locators (URL)" by T. Berners-Lee, L. Masinter, M. McCahill, December 1994 RFC 3986 is considered the current standard and any future changes to urlparse module should conform with it. The urlparse module is currently not entirely compliant with this RFC due to defacto scenarios for parsing, and for backward compatibility purposes, some parsing quirks from older RFCs are retained. The testcases in test_urlparse.py provides a good indicator of parsing behavior. """ import re import sys import collections __all__ = ["urlparse", "urlunparse", "urljoin", "urldefrag", "urlsplit", "urlunsplit", "urlencode", "parse_qs", "parse_qsl", "quote", "quote_plus", "quote_from_bytes", "unquote", "unquote_plus", "unquote_to_bytes", "DefragResult", "ParseResult", "SplitResult", "DefragResultBytes", "ParseResultBytes", "SplitResultBytes"] # A classification of schemes (‘‘ means apply by default) uses_relative = [‘ftp‘, ‘http‘, ‘gopher‘, ‘nntp‘, ‘imap‘, ‘wais‘, ‘file‘, ‘https‘, ‘shttp‘, ‘mms‘, ‘prospero‘, ‘rtsp‘, ‘rtspu‘, ‘‘, ‘sftp‘, ‘svn‘, ‘svn+ssh‘] uses_netloc = [‘ftp‘, ‘http‘, ‘gopher‘, ‘nntp‘, ‘telnet‘, ‘imap‘, ‘wais‘, ‘file‘, ‘mms‘, ‘https‘, ‘shttp‘, ‘snews‘, ‘prospero‘, ‘rtsp‘, ‘rtspu‘, ‘rsync‘, ‘‘, ‘svn‘, ‘svn+ssh‘, ‘sftp‘, ‘nfs‘, ‘git‘, ‘git+ssh‘] uses_params = [‘ftp‘, ‘hdl‘, ‘prospero‘, ‘http‘, ‘imap‘, ‘https‘, ‘shttp‘, ‘rtsp‘, ‘rtspu‘, ‘sip‘, ‘sips‘, ‘mms‘, ‘‘, ‘sftp‘, ‘tel‘] # These are not actually used anymore, but should stay for backwards # compatibility. (They are undocumented, but have a public-looking name.) non_hierarchical = [‘gopher‘, ‘hdl‘, ‘mailto‘, ‘news‘, ‘telnet‘, ‘wais‘, ‘imap‘, ‘snews‘, ‘sip‘, ‘sips‘] uses_query = [‘http‘, ‘wais‘, ‘imap‘, ‘https‘, ‘shttp‘, ‘mms‘, ‘gopher‘, ‘rtsp‘, ‘rtspu‘, ‘sip‘, ‘sips‘, ‘‘] uses_fragment = [‘ftp‘, ‘hdl‘, ‘http‘, ‘gopher‘, ‘news‘, ‘nntp‘, ‘wais‘, ‘https‘, ‘shttp‘, ‘snews‘, ‘file‘, ‘prospero‘, ‘‘] # Characters valid in scheme names scheme_chars = (‘abcdefghijklmnopqrstuvwxyz‘ ‘ABCDEFGHIJKLMNOPQRSTUVWXYZ‘ ‘0123456789‘ ‘+-.‘) # XXX: Consider replacing with functools.lru_cache MAX_CACHE_SIZE = 20 _parse_cache = {} def clear_cache(): """Clear the parse cache and the quoters cache.""" _parse_cache.clear() _safe_quoters.clear() # Helpers for bytes handling # For 3.2, we deliberately require applications that # handle improperly quoted URLs to do their own # decoding and encoding. If valid use cases are # presented, we may relax this by using latin-1 # decoding internally for 3.3 _implicit_encoding = ‘ascii‘ _implicit_errors = ‘strict‘ def _noop(obj): return obj def _encode_result(obj, encoding=_implicit_encoding, errors=_implicit_errors): return obj.encode(encoding, errors) def _decode_args(args, encoding=_implicit_encoding, errors=_implicit_errors): return tuple(x.decode(encoding, errors) if x else ‘‘ for x in args) def _coerce_args(*args): # Invokes decode if necessary to create str args # and returns the coerced inputs along with # an appropriate result coercion function # - noop for str inputs # - encoding function otherwise str_input = isinstance(args[0], str) for arg in args[1:]: # We special-case the empty string to support the # "scheme=‘‘" default argument to some functions if arg and isinstance(arg, str) != str_input: raise TypeError("Cannot mix str and non-str arguments") if str_input: return args + (_noop,) return _decode_args(args) + (_encode_result,) # Result objects are more helpful than simple tuples class _ResultMixinStr(object): """Standard approach to encoding parsed results from str to bytes""" __slots__ = () def encode(self, encoding=‘ascii‘, errors=‘strict‘): return self._encoded_counterpart(*(x.encode(encoding, errors) for x in self)) class _ResultMixinBytes(object): """Standard approach to decoding parsed results from bytes to str""" __slots__ = () def decode(self, encoding=‘ascii‘, errors=‘strict‘): return self._decoded_counterpart(*(x.decode(encoding, errors) for x in self)) class _NetlocResultMixinBase(object): """Shared methods for the parsed result objects containing a netloc element""" __slots__ = () @property def username(self): return self._userinfo[0] @property def password(self): return self._userinfo[1] @property def hostname(self): hostname = self._hostinfo[0] if not hostname: hostname = None elif hostname is not None: hostname = hostname.lower() return hostname @property def port(self): port = self._hostinfo[1] if port is not None: port = int(port, 10) # Return None on an illegal port if not ( 0 <= port <= 65535): return None return port class _NetlocResultMixinStr(_NetlocResultMixinBase, _ResultMixinStr): __slots__ = () @property def _userinfo(self): netloc = self.netloc userinfo, have_info, hostinfo = netloc.rpartition(‘@‘) if have_info: username, have_password, password = userinfo.partition(‘:‘) if not have_password: password = None else: username = password = None return username, password @property def _hostinfo(self): netloc = self.netloc _, _, hostinfo = netloc.rpartition(‘@‘) _, have_open_br, bracketed = hostinfo.partition(‘[‘) if have_open_br: hostname, _, port = bracketed.partition(‘]‘) _, _, port = port.partition(‘:‘) else: hostname, _, port = hostinfo.partition(‘:‘) if not port: port = None return hostname, port class _NetlocResultMixinBytes(_NetlocResultMixinBase, _ResultMixinBytes): __slots__ = () @property def _userinfo(self): netloc = self.netloc userinfo, have_info, hostinfo = netloc.rpartition(b‘@‘) if have_info: username, have_password, password = userinfo.partition(b‘:‘) if not have_password: password = None else: username = password = None return username, password @property def _hostinfo(self): netloc = self.netloc _, _, hostinfo = netloc.rpartition(b‘@‘) _, have_open_br, bracketed = hostinfo.partition(b‘[‘) if have_open_br: hostname, _, port = bracketed.partition(b‘]‘) _, _, port = port.partition(b‘:‘) else: hostname, _, port = hostinfo.partition(b‘:‘) if not port: port = None return hostname, port from collections import namedtuple _DefragResultBase = namedtuple(‘DefragResult‘, ‘url fragment‘) _SplitResultBase = namedtuple(‘SplitResult‘, ‘scheme netloc path query fragment‘) _ParseResultBase = namedtuple(‘ParseResult‘, ‘scheme netloc path params query fragment‘) # For backwards compatibility, alias _NetlocResultMixinStr # ResultBase is no longer part of the documented API, but it is # retained since deprecating it isn‘t worth the hassle ResultBase = _NetlocResultMixinStr # Structured result objects for string data class DefragResult(_DefragResultBase, _ResultMixinStr): __slots__ = () def geturl(self): if self.fragment: return self.url + ‘#‘ + self.fragment else: return self.url class SplitResult(_SplitResultBase, _NetlocResultMixinStr): __slots__ = () def geturl(self): return urlunsplit(self) class ParseResult(_ParseResultBase, _NetlocResultMixinStr): __slots__ = () def geturl(self): return urlunparse(self) # Structured result objects for bytes data class DefragResultBytes(_DefragResultBase, _ResultMixinBytes): __slots__ = () def geturl(self): if self.fragment: return self.url + b‘#‘ + self.fragment else: return self.url class SplitResultBytes(_SplitResultBase, _NetlocResultMixinBytes): __slots__ = () def geturl(self): return urlunsplit(self) class ParseResultBytes(_ParseResultBase, _NetlocResultMixinBytes): __slots__ = () def geturl(self): return urlunparse(self) # Set up the encode/decode result pairs def _fix_result_transcoding(): _result_pairs = ( (DefragResult, DefragResultBytes), (SplitResult, SplitResultBytes), (ParseResult, ParseResultBytes), ) for _decoded, _encoded in _result_pairs: _decoded._encoded_counterpart = _encoded _encoded._decoded_counterpart = _decoded _fix_result_transcoding() del _fix_result_transcoding def urlparse(url, scheme=‘‘, allow_fragments=True): """Parse a URL into 6 components: <scheme>://<netloc>/<path>;<params>?<query>#<fragment> Return a 6-tuple: (scheme, netloc, path, params, query, fragment). Note that we don‘t break the components up in smaller bits (e.g. netloc is a single string) and we don‘t expand % escapes.""" url, scheme, _coerce_result = _coerce_args(url, scheme) splitresult = urlsplit(url, scheme, allow_fragments) scheme, netloc, url, query, fragment = splitresult if scheme in uses_params and ‘;‘ in url: url, params = _splitparams(url) else: params = ‘‘ result = ParseResult(scheme, netloc, url, params, query, fragment) return _coerce_result(result) def _splitparams(url): if ‘/‘ in url: i = url.find(‘;‘, url.rfind(‘/‘)) if i < 0: return url, ‘‘ else: i = url.find(‘;‘) return url[:i], url[i+1:] def _splitnetloc(url, start=0): delim = len(url) # position of end of domain part of url, default is end for c in ‘/?#‘: # look for delimiters; the order is NOT important wdelim = url.find(c, start) # find first of this delim if wdelim >= 0: # if found delim = min(delim, wdelim) # use earliest delim position return url[start:delim], url[delim:] # return (domain, rest) def urlsplit(url, scheme=‘‘, allow_fragments=True): """Parse a URL into 5 components: <scheme>://<netloc>/<path>?<query>#<fragment> Return a 5-tuple: (scheme, netloc, path, query, fragment). Note that we don‘t break the components up in smaller bits (e.g. netloc is a single string) and we don‘t expand % escapes.""" url, scheme, _coerce_result = _coerce_args(url, scheme) allow_fragments = bool(allow_fragments) key = url, scheme, allow_fragments, type(url), type(scheme) cached = _parse_cache.get(key, None) if cached: return _coerce_result(cached) if len(_parse_cache) >= MAX_CACHE_SIZE: # avoid runaway growth clear_cache() netloc = query = fragment = ‘‘ i = url.find(‘:‘) if i > 0: if url[:i] == ‘http‘: # optimize the common case scheme = url[:i].lower() url = url[i+1:] if url[:2] == ‘//‘: netloc, url = _splitnetloc(url, 2) if ((‘[‘ in netloc and ‘]‘ not in netloc) or (‘]‘ in netloc and ‘[‘ not in netloc)): raise ValueError("Invalid IPv6 URL") if allow_fragments and ‘#‘ in url: url, fragment = url.split(‘#‘, 1) if ‘?‘ in url: url, query = url.split(‘?‘, 1) v = SplitResult(scheme, netloc, url, query, fragment) _parse_cache[key] = v return _coerce_result(v) for c in url[:i]: if c not in scheme_chars: break else: # make sure "url" is not actually a port number (in which case # "scheme" is really part of the path) rest = url[i+1:] if not rest or any(c not in ‘0123456789‘ for c in rest): # not a port number scheme, url = url[:i].lower(), rest if url[:2] == ‘//‘: netloc, url = _splitnetloc(url, 2) if ((‘[‘ in netloc and ‘]‘ not in netloc) or (‘]‘ in netloc and ‘[‘ not in netloc)): raise ValueError("Invalid IPv6 URL") if allow_fragments and ‘#‘ in url: url, fragment = url.split(‘#‘, 1) if ‘?‘ in url: url, query = url.split(‘?‘, 1) v = SplitResult(scheme, netloc, url, query, fragment) _parse_cache[key] = v return _coerce_result(v) def urlunparse(components): """Put a parsed URL back together again. This may result in a slightly different, but equivalent URL, if the URL that was parsed originally had redundant delimiters, e.g. a ? with an empty query (the draft states that these are equivalent).""" scheme, netloc, url, params, query, fragment, _coerce_result = ( _coerce_args(*components)) if params: url = "%s;%s" % (url, params) return _coerce_result(urlunsplit((scheme, netloc, url, query, fragment))) def urlunsplit(components): """Combine the elements of a tuple as returned by urlsplit() into a complete URL as a string. The data argument can be any five-item iterable. This may result in a slightly different, but equivalent URL, if the URL that was parsed originally had unnecessary delimiters (for example, a ? with an empty query; the RFC states that these are equivalent).""" scheme, netloc, url, query, fragment, _coerce_result = ( _coerce_args(*components)) if netloc or (scheme and scheme in uses_netloc and url[:2] != ‘//‘): if url and url[:1] != ‘/‘: url = ‘python爬虫入门urllib库的使用