robotparser.py

""" robotparser.py

    Copyright (C) 2000  Bastian Kleineidam

    You can choose between two licenses when using this package:
    1) GNU GPLv2
    2) PSF license for Python 2.2

    The robots.txt Exclusion Protocol is implemented as specified in
    http://info.webcrawler.com/mak/projects/robots/norobots-rfc.html
"""
import urlparse
import urllib

__all__ = ["RobotFileParser"]


class RobotFileParser:
    """ This class provides a set of methods to read, parse and answer
    questions about a single robots.txt file.

    """

    def __init__(self, url=''):
        self.entries = []
        self.default_entry = None
        self.disallow_all = False
        self.allow_all = False
        self.set_url(url)
        self.last_checked = 0

    def mtime(self):
        """Returns the time the robots.txt file was last fetched.

        This is useful for long-running web spiders that need to
        check for new robots.txt files periodically.

        """
        return self.last_checked

    def modified(self):
        """Sets the time the robots.txt file was last fetched to the
        current time.

        """
        import time
        self.last_checked = time.time()

    def set_url(self, url):
        """Sets the URL referring to a robots.txt file."""
        self.url = url
        self.host, self.path = urlparse.urlparse(url)[1:3]

    def read(self):
        """Reads the robots.txt URL and feeds it to the parser."""
        opener = URLopener()
        f = opener.open(self.url)
        lines = [line.strip() for line in f]
        f.close()
        self.errcode = opener.errcode
        if self.errcode in (401, 403):
            self.disallow_all = True
        elif self.errcode >= 400:
            self.allow_all = True
        elif self.errcode == 200 and lines:
            self.parse(lines)

    def _add_entry(self, entry):
        if "*" in entry.useragents:
            # the default entry is considered last
            self.default_entry = entry
        else:
            self.entries.append(entry)

    def parse(self, lines):
        """parse the input lines from a robots.txt file.
           We allow that a user-agent: line is not preceded by
           one or more blank lines."""
        # states:
        #   0: start state
        #   1: saw user-agent line
        #   2: saw an allow or disallow line
        state = 0
        linenumber = 0
        entry = Entry()

        for line in lines:
            linenumber += 1
            if not line:
                if state == 1:
                    entry = Entry()
                    state = 0
                elif state == 2:
                    self._add_entry(entry)
                    entry = Entry()
                    state = 0
            # remove optional comment and strip line
            i = line.find('#')
            if i >= 0:
                line = line[:i]
            line = line.strip()
            if not line:
                continue
            line = line.split(':', 1)
            if len(line) == 2:
                line[0] = line[0].strip().lower()
                line[1] = urllib.unquote(line[1].strip())
                if line[0] == "user-agent":
                    if state == 2:
                        self._add_entry(entry)
                        entry = Entry()
                    entry.useragents.append(line[1])
                    state = 1
                elif line[0] == "disallow":
                    if state != 0:
                        entry.rulelines.append(RuleLine(line[1], False))
                        state = 2
                elif line[0] == "allow":
                    if state != 0:
                        entry.rulelines.append(RuleLine(line[1], True))
                        state = 2
        if state == 2:
            self.entries.append(entry)


    def can_fetch(self, useragent, url):
        """using the parsed robots.txt decide if useragent can fetch url"""
        if self.disallow_all:
            return False
        if self.allow_all:
            return True
        # search for given user agent matches
        # the first match counts
        url = urllib.quote(urlparse.urlparse(urllib.unquote(url))[2]) or "/"
        for entry in self.entries:
            if entry.applies_to(useragent):
                return entry.allowance(url)
        # try the default entry last
        if self.default_entry:
            return self.default_entry.allowance(url)
        # agent not found ==> access granted
        return True


    def __str__(self):
        return ''.join([str(entry) + "\n" for entry in self.entries])


class RuleLine:
    """A rule line is a single "Allow:" (allowance==True) or "Disallow:"
       (allowance==False) followed by a path."""
    def __init__(self, path, allowance):
        if path == '' and not allowance:
            # an empty value means allow all
            allowance = True
        self.path = urllib.quote(path)
        self.allowance = allowance

    def applies_to(self, filename):
        return self.path == "*" or filename.startswith(self.path)

    def __str__(self):
        return (self.allowance and "Allow" or "Disallow") + ": " + self.path


class Entry:
    """An entry has one or more user-agents and zero or more rulelines"""
    def __init__(self):
        self.useragents = []
        self.rulelines = []

    def __str__(self):
        ret = []
        for agent in self.useragents:
            ret.extend(["User-agent: ", agent, "\n"])
        for line in self.rulelines:
            ret.extend([str(line), "\n"])
        return ''.join(ret)

    def applies_to(self, useragent):
        """check if this entry applies to the specified agent"""
        # split the name token and make it lower case
        useragent = useragent.split("/")[0].lower()
        for agent in self.useragents:
            if agent == '*':
                # we have the catch-all agent
                return True
            agent = agent.lower()
            if agent in useragent:
                return True
        return False

    def allowance(self, filename):
        """Preconditions:
        - our agent applies to this entry
        - filename is URL decoded"""
        for line in self.rulelines:
            if line.applies_to(filename):
                return line.allowance
        return True

class URLopener(urllib.FancyURLopener):
    def __init__(self, *args):
        urllib.FancyURLopener.__init__(self, *args)
        self.errcode = 200

    def prompt_user_passwd(self, host, realm):
        ## If robots.txt file is accessible only with a password,
        ## we act as if the file wasn't there.
        return None, None

    def http_error_default(self, url, fp, errcode, errmsg, headers):
        self.errcode = errcode
        return urllib.FancyURLopener.http_error_default(self, url, fp, errcode,
                                                        errmsg, headers)