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259 lines
8.6 KiB
Python
259 lines
8.6 KiB
Python
3 weeks ago
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""" robotparser.py
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Copyright (C) 2000 Bastian Kleineidam
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You can choose between two licenses when using this package:
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1) GNU GPLv2
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2) PSF license for Python 2.2
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The robots.txt Exclusion Protocol is implemented as specified in
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http://www.robotstxt.org/norobots-rfc.txt
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"""
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import collections
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import urllib.parse
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import urllib.request
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__all__ = ["RobotFileParser"]
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RequestRate = collections.namedtuple("RequestRate", "requests seconds")
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class RobotFileParser:
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""" This class provides a set of methods to read, parse and answer
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questions about a single robots.txt file.
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"""
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def __init__(self, url=''):
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self.entries = []
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self.default_entry = None
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self.disallow_all = False
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self.allow_all = False
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self.set_url(url)
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self.last_checked = 0
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def mtime(self):
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"""Returns the time the robots.txt file was last fetched.
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This is useful for long-running web spiders that need to
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check for new robots.txt files periodically.
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"""
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return self.last_checked
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def modified(self):
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"""Sets the time the robots.txt file was last fetched to the
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current time.
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"""
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import time
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self.last_checked = time.time()
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def set_url(self, url):
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"""Sets the URL referring to a robots.txt file."""
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self.url = url
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self.host, self.path = urllib.parse.urlparse(url)[1:3]
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def read(self):
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"""Reads the robots.txt URL and feeds it to the parser."""
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try:
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f = urllib.request.urlopen(self.url)
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except urllib.error.HTTPError as err:
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if err.code in (401, 403):
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self.disallow_all = True
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elif err.code >= 400 and err.code < 500:
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self.allow_all = True
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else:
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raw = f.read()
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self.parse(raw.decode("utf-8").splitlines())
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def _add_entry(self, entry):
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if "*" in entry.useragents:
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# the default entry is considered last
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if self.default_entry is None:
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# the first default entry wins
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self.default_entry = entry
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else:
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self.entries.append(entry)
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def parse(self, lines):
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"""Parse the input lines from a robots.txt file.
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We allow that a user-agent: line is not preceded by
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one or more blank lines.
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"""
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# states:
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# 0: start state
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# 1: saw user-agent line
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# 2: saw an allow or disallow line
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state = 0
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entry = Entry()
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self.modified()
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for line in lines:
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if not line:
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if state == 1:
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entry = Entry()
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state = 0
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elif state == 2:
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self._add_entry(entry)
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entry = Entry()
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state = 0
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# remove optional comment and strip line
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i = line.find('#')
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if i >= 0:
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line = line[:i]
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line = line.strip()
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if not line:
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continue
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line = line.split(':', 1)
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if len(line) == 2:
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line[0] = line[0].strip().lower()
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line[1] = urllib.parse.unquote(line[1].strip())
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if line[0] == "user-agent":
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if state == 2:
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self._add_entry(entry)
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entry = Entry()
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entry.useragents.append(line[1])
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state = 1
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elif line[0] == "disallow":
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if state != 0:
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entry.rulelines.append(RuleLine(line[1], False))
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state = 2
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elif line[0] == "allow":
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if state != 0:
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entry.rulelines.append(RuleLine(line[1], True))
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state = 2
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elif line[0] == "crawl-delay":
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if state != 0:
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# before trying to convert to int we need to make
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# sure that robots.txt has valid syntax otherwise
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# it will crash
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if line[1].strip().isdigit():
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entry.delay = int(line[1])
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state = 2
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elif line[0] == "request-rate":
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if state != 0:
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numbers = line[1].split('/')
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# check if all values are sane
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if (len(numbers) == 2 and numbers[0].strip().isdigit()
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and numbers[1].strip().isdigit()):
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entry.req_rate = RequestRate(int(numbers[0]), int(numbers[1]))
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state = 2
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if state == 2:
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self._add_entry(entry)
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def can_fetch(self, useragent, url):
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"""using the parsed robots.txt decide if useragent can fetch url"""
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if self.disallow_all:
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return False
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if self.allow_all:
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return True
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# Until the robots.txt file has been read or found not
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# to exist, we must assume that no url is allowable.
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# This prevents false positives when a user erroneously
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# calls can_fetch() before calling read().
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if not self.last_checked:
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return False
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# search for given user agent matches
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# the first match counts
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parsed_url = urllib.parse.urlparse(urllib.parse.unquote(url))
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url = urllib.parse.urlunparse(('','',parsed_url.path,
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parsed_url.params,parsed_url.query, parsed_url.fragment))
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url = urllib.parse.quote(url)
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if not url:
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url = "/"
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for entry in self.entries:
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if entry.applies_to(useragent):
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return entry.allowance(url)
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# try the default entry last
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if self.default_entry:
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return self.default_entry.allowance(url)
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# agent not found ==> access granted
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return True
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def crawl_delay(self, useragent):
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if not self.mtime():
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return None
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for entry in self.entries:
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if entry.applies_to(useragent):
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return entry.delay
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return self.default_entry.delay
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def request_rate(self, useragent):
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if not self.mtime():
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return None
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for entry in self.entries:
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if entry.applies_to(useragent):
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return entry.req_rate
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return self.default_entry.req_rate
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def __str__(self):
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entries = self.entries
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if self.default_entry is not None:
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entries = entries + [self.default_entry]
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return '\n'.join(map(str, entries)) + '\n'
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class RuleLine:
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"""A rule line is a single "Allow:" (allowance==True) or "Disallow:"
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(allowance==False) followed by a path."""
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def __init__(self, path, allowance):
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if path == '' and not allowance:
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# an empty value means allow all
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allowance = True
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path = urllib.parse.urlunparse(urllib.parse.urlparse(path))
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self.path = urllib.parse.quote(path)
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self.allowance = allowance
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def applies_to(self, filename):
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return self.path == "*" or filename.startswith(self.path)
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def __str__(self):
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return ("Allow" if self.allowance else "Disallow") + ": " + self.path
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class Entry:
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"""An entry has one or more user-agents and zero or more rulelines"""
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def __init__(self):
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self.useragents = []
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self.rulelines = []
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self.delay = None
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self.req_rate = None
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def __str__(self):
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ret = []
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for agent in self.useragents:
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ret.append(f"User-agent: {agent}")
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if self.delay is not None:
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ret.append(f"Crawl-delay: {self.delay}")
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if self.req_rate is not None:
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rate = self.req_rate
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ret.append(f"Request-rate: {rate.requests}/{rate.seconds}")
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ret.extend(map(str, self.rulelines))
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ret.append('') # for compatibility
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return '\n'.join(ret)
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def applies_to(self, useragent):
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"""check if this entry applies to the specified agent"""
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# split the name token and make it lower case
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useragent = useragent.split("/")[0].lower()
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for agent in self.useragents:
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if agent == '*':
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# we have the catch-all agent
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return True
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agent = agent.lower()
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if agent in useragent:
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return True
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return False
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def allowance(self, filename):
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"""Preconditions:
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- our agent applies to this entry
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- filename is URL decoded"""
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for line in self.rulelines:
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if line.applies_to(filename):
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return line.allowance
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return True
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