python 解析 crontab

1. 使用croniter

官方教程是：https://github.com/taichino/croniter

示例一：获得下次crontab执行的时间

　　

from croniter import croniter
from datetime import datetime
print datetime.now()

cron = croniter('01 */5 * * * *', datetime.now())  
print(cron.get_next(datetime))


输出结果是：

2021-03-12 13:52:10.627000
2021-03-12 15:01:00

示例二：计算当前一段时间以后的 crontab执行时间

　　直接上代码

　　

from croniter import croniter_range
from datetime import datetime,timedelta
tomorrow = datetime.strptime((datetime.now() + timedelta(days=2)).strftime('%Y-%m-%d %H:%M:%S'), "%Y-%m-%d %H:%M:%S")
print "tomorrow",tomorrow
print type(tomorrow)
for run_time in croniter_range(datetime.now(), tomorrow, "01 */2 * * *"):
    print(run_time)

　　输入结果：

　　

C:Python27python2.exe F:/SpeedCrawlerEnd/crawler_algorithm/rwdd/apscheduler_test.py
tomorrow 2021-03-14 13:57:17
<type 'datetime.datetime'>
2021-03-12 14:01:00
2021-03-12 16:01:00
2021-03-12 18:01:00
2021-03-12 20:01:00
2021-03-12 22:01:00
2021-03-13 00:01:00
2021-03-13 02:01:00
2021-03-13 04:01:00
2021-03-13 06:01:00
2021-03-13 08:01:00
2021-03-13 10:01:00
2021-03-13 12:01:00
2021-03-13 14:01:00
2021-03-13 16:01:00
2021-03-13 18:01:00
2021-03-13 20:01:00
2021-03-13 22:01:00
2021-03-14 00:01:00
2021-03-14 02:01:00
2021-03-14 04:01:00
2021-03-14 06:01:00
2021-03-14 08:01:00
2021-03-14 10:01:00
2021-03-14 12:01:00

示例三：直接上代码

　　 

代码一：


from datetime import datetime
import time
import croniter


def run_get_next_time(sched):
    datetime_now = datetime.now()
    print [croniter.croniter(sched, datetime_now).get_next(datetime).strftime("%Y-%m-%d %H:%M:%S") for page in range(10)]



代码二：


def run_get_next_time(sched):
    datetime_now = datetime.now()
    for page in range(10):
        cron = croniter.croniter(sched, datetime_now)
        datetime_now = cron.get_next(datetime)
            # .strftime("%Y-%m-%d %H:%M:%S")
        print datetime_now
        print type(datetime_now)
        # time.sleep(2222)
sched = "10 */2 * * * "

使用github 开源  crontab_parser

直接上代码，新建python文件，文件名 crontab_parser  ，crontab_parser文件代码如下

　　　　

# -*- coding: utf-8 -*-

#
# import croniter
# from datetime import datetime
#
# import croniter
# import datetime
#
#
# def run_get_next_time(sched):
#     cron = croniter.croniter(sched, datetime.datetime.now())
#     print "cron", cron.get_next(ret_type=10)
#
#     return cron.get_next(ret_type=10).strftime("%Y-%m-%d %H:%M")
#
#
# # for page in range(10):
# #     print(run_get_next_time("10 */2 * * * "))
#
#
# from crontab import CronTab
# from datetime import datetime
#
# # define the crontab for 25 minutes past the hour every hour
# entry = CronTab('25 */2 * * *')
# # find the delay from when this was run (around 11:13AM)
# print entry.next(default_utc=False)
# import time
#
# time.sleep(60)

import re
import datetime


class SimpleCrontabEntry(object):
    """Contrab-like parser.
    Only deals with the first 5 fields of a normal crontab
    entry."""

    def __init__(self, entry, expiration=0):
        self.__setup_timespec()
        self.set_value(entry)
        self.set_expiration(expiration)

    def set_expiration(self, val):
        self.expiration = datetime.timedelta(minutes=val)

    def set_value(self, entry):
        self.data = entry
        fields = re.findall("S+", self.data)
        if len(fields) != 5:
            raise ValueError("Crontab entry needs 5 fields")
        self.fields = {
            "minute": fields[0],
            "hour": fields[1],
            "day": fields[2],
            "month": fields[3],
            "weekday": fields[4],
        }
        if not self._is_valid():
            raise ValueError("Bad Entry")

    #### HERE BEGINS THE CODE BORROWED FROM gnome-schedule ###
    def __setup_timespec(self):

        self.special = {
            "@reboot": '',
            "@hourly": '0 * * * *',
            "@daily": '0 0 * * *',
            "@weekly": '0 0 * * 0',
            "@monthly": '0 0 1 * *',
            "@yearly": '0 0 1 1 *'
        }

        self.timeranges = {
            "minute": range(0, 60),
            "hour": range(0, 24),
            "day": range(1, 32),
            "month": range(1, 13),
            "weekday": range(0, 8)
        }

        self.timenames = {
            "minute": "Minute",
            "hour": "Hour",
            "day": "Day of Month",
            "month": "Month",
            "weekday": "Weekday"
        }

        self.monthnames = {
            "1": "Jan",
            "2": "Feb",
            "3": "Mar",
            "4": "Apr",
            "5": "May",
            "6": "Jun",
            "7": "Jul",
            "8": "Aug",
            "9": "Sep",
            "10": "Oct",
            "11": "Nov",
            "12": "Dec"
        }

        self.downames = {
            "0": "Sun",
            "1": "Mon",
            "2": "Tue",
            "3": "Wed",
            "4": "Thu",
            "5": "Fri",
            "6": "Sat",
            "7": "Sun"
        }

    def checkfield(self, expr, type):
        """Verifies format of Crontab timefields
        Checks a single Crontab time expression.
        At first possibly contained alias names will be replaced by their
        corresponding numbers. After that every asterisk will be replaced by
        a "first to last" expression. Then the expression will be splitted
        into the komma separated subexpressions.
        Each subexpression will run through:
        1. Check for stepwidth in range (if it has one)
        2. Check for validness of range-expression (if it is one)
        3. If it is no range: Check for simple numeric
        4. If it is numeric: Check if it's in range
        If one of this checks failed, an exception is raised. Otherwise it will
        do nothing. Therefore this function should be used with
        a try/except construct.
        """

        timerange = self.timeranges[type]

        # Replace alias names only if no leading and following alphanumeric and
        # no leading slash is present. Otherwise terms like "JanJan" or
        # "1Feb" would give a valid check. Values after a slash are stepwidths
        # and shouldn't have an alias.
        if type == "month":
            alias = self.monthnames.copy()
        elif type == "weekday":
            alias = self.downames.copy()
        else:
            alias = None
        if alias != None:
            while True:
                try:
                    key, value = alias.popitem()
                except KeyError:
                    break
                expr = re.sub("(?<!w|/)" + value + "(?!w)", key, expr)

        expr = expr.replace("*", str(min(timerange)) + "-" + str(max(timerange)))

        lst = expr.split(",")
        rexp_step = re.compile("^(d+-d+)/(d+)$")
        rexp_range = re.compile("^(d+)-(d+)$")

        expr_range = []
        for field in lst:
            # Extra variables for time calculation
            step = None
            buff = None

            result = rexp_step.match(field)
            if result != None:
                field = result.groups()[0]
                # We need to take step in count
                step = int(result.groups()[1])
                if step not in timerange:
                    raise ValueError("stepwidth",
                                     self.timenames[type],
                                     "Must be between %(min)s and %(max)s" % {"min": min(timerange),
                                                                              "max": max(timerange)})

            result = rexp_range.match(field)
            if (result != None):
                if (int(result.groups()[0]) not in timerange) or (int(result.groups()[1]) not in timerange):
                    raise ValueError("range",
                                     self.timenames[type],
                                     "Must be between %(min)s and %(max)s" % {"min": min(timerange),
                                                                              "max": max(timerange)})
                # Now we deal with a range...
                if step != None:
                    buff = range(int(result.groups()[0]), int(result.groups()[1]) + 1, step)
                else:
                    buff = range(int(result.groups()[0]), int(result.groups()[1]) + 1)

            elif not field.isdigit():
                raise ValueError("fixed",
                                 self.timenames[type],
                                 "%s is not a number" % (field))
            elif int(field) not in timerange:
                raise ValueError("fixed",
                                 self.timenames[type],
                                 "Must be between %(min)s and %(max)s" % {"min": min(timerange),
                                                                          "max": max(timerange)})
            if buff != None:
                expr_range.extend(buff)
            else:
                expr_range.append(int(field))

        expr_range.sort()
        # Here we may need to check wether some elements have duplicates
        self.fields[type] = expr_range

    #### HERE ENDS THE CODE BORROWED FROM gnome-schedule ###

    def _is_valid(self):
        """Validates the data to check for a well-formated cron
        entry.
        Returns True or false"""

        try:
            for typ, exp in self.fields.items():
                self.checkfield(exp, typ)
        except ValueError, (specific, caused, explanation):
            print "PROBLEM TYPE: %s, ON FIELD: %s -> %s " % (specific, caused, explanation)
            return False
        return True

    def __next_time(self, time_list, time_now):
        """Little helper function to find next element on the list"""
        tmp = [x for x in time_list if x >= time_now]
        carry = False
        if len(tmp) == 0:
            carry = True
            sol = time_list[0]
        else:
            sol = tmp[0]
        return sol, carry

    def __prev_time(self, time_list, item):
        """Little helper function to find previous element on the list"""
        pos = time_list.index(item)
        elem = time_list[pos - 1]
        carry = elem >= time_list[pos]
        return elem, carry

    def __next_month(self, month, sol):
        """Find next month of execution given the month arg. If month
        is different than current calls all the other __next_*
        functions to set up the time."""

        sol['month'], carry = self.__next_time(self.fields['month'], month)
        if carry:
            sol['year'] += 1
        if sol['month'] != month:
            self.__next_day(1, sol)
            self.__next_hour(0, sol)
            self.__next_minute(0, sol)
            return False
        return True

    def __next_minute(self, minute, sol):
        """Find next minute of execution given the minute arg."""
        sol['minute'], carry = self.__next_time(self.fields['minute'], minute)
        if carry:
            self.__next_hour(sol['hour'] + 1, sol)
        return True

    def __next_hour(self, hour, sol):
        """Find next hour of execution given the hour arg. If hour is
        different than current calls the __next_hour function to set
        up the minute """

        sol['hour'], carry = self.__next_time(self.fields['hour'], hour)
        if carry:
            self.__next_day(sol['day'] + 1, sol)
        if sol['hour'] != hour:
            self.__next_minute(0, sol)
            return False
        return True

    # el weekday se calcula a partir del dia, el mes y ao dentro de sol
    def __next_day(self, day, sol):
        """Find next day of execution given the day and the month/year
        information held on the sol arg. If day is different than
        current calls __next_hour and __next_minute functions to set
        them to the correct values"""

        try:
            now = datetime.date(sol['year'], sol['month'], day)
        except:
            try:
                now = datetime.date(sol['year'], sol['month'] + 1, 1)
            except:
                now = datetime.date(sol['year'] + 1, 1, 1)
        # The way is handled on the system is monday = 0, but for crontab sunday =0
        weekday = now.weekday() + 1
        # first calculate day
        day_tmp, day_carry = self.__next_time(self.fields['day'], day)
        day_diff = datetime.date(sol['year'], sol['month'], day_tmp) - now

        # if we have all days but we don't have all weekdays we need to
        # perform different
        if len(self.fields['day']) == 31 and len(self.fields['weekday']) != 8:
            weekday_tmp, weekday_carry = self.__next_time(self.fields['weekday'], weekday)
            # Both 0 and 7 represent sunday
            weekday_tmp -= 1
            if weekday_tmp < 0: weekday_tmp = 6
            weekday_diff = datetime.timedelta(days=weekday_tmp - (weekday - 1))
            if weekday_carry:
                weekday_diff += datetime.timedelta(weeks=1)
            weekday_next_month = (now + weekday_diff).month != now.month
            # If next weekday is not on the next month
            if not weekday_next_month:
                sol['day'] = (now + weekday_diff).day
                if sol['day'] != day:
                    self.__next_hour(0, sol)
                    self.__next_minute(0, sol)
                    return False
                return True
            else:
                flag = self.__next_month(sol['month'] + 1, sol)
                if flag:
                    return self.__next_day(0, sol)
                return False

        # if we don't have all the weekdays means that we need to use
        # them to calculate next day
        if len(self.fields['weekday']) != 8:
            weekday_tmp, weekday_carry = self.__next_time(self.fields['weekday'], weekday)
            # Both 0 and 7 represent sunday
            weekday_tmp -= 1
            if weekday_tmp < 0: weekday_tmp = 6
            weekday_diff = datetime.timedelta(days=weekday_tmp - (weekday - 1))
            if weekday_carry:
                weekday_diff += datetime.timedelta(weeks=1)
            weekday_next_month = (now + weekday_diff).month != now.month
            # If next weekday is not on the next month
            if not weekday_next_month:
                #  If the next day is on other month, the next weekday
                #  is closer to happen so is what we choose
                if day_carry:
                    sol['day'] = (now + weekday_diff).day
                    if sol['day'] != day:
                        self.__next_hour(0, sol)
                        self.__next_minute(0, sol)
                        return False
                    return True
                else:
                    # Both day and weekday are good candidates, let's
                    # find out who is going to happen
                    # sooner
                    diff = min(day_diff, weekday_diff)
                    sol['day'] = (now + diff).day
                    if sol['day'] != day:
                        self.__next_hour(0, sol)
                        self.__next_minute(0, sol)
                        return False
                    return True

        sol['day'] = day_tmp
        if day_carry:
            self.__next_month(sol['month'] + 1, sol)
        if sol['day'] != day:
            self.__next_hour(0, sol)
            self.__next_minute(0, sol)
            return False
        return True

    def matches(self, time=datetime.datetime.now()):
        """Checks if given time matches cron pattern."""
        return time.month in self.fields['month'] and 
               time.day in self.fields['day'] and 
               time.hour in self.fields['hour'] and 
               time.minute in self.fields['minute'] and 
               time.weekday() + 1 in [d or 7 for d in
                                      self.fields['weekday']]  # Sunday may be represented as ``0`` or ``7``.

    def next_run(self, time=datetime.datetime.now()):
        """Calculates when will the next execution be."""
        if self.matches(time):
            time += datetime.timedelta(minutes=1)
        sol = {'minute': time.minute, 'hour': time.hour, 'day': time.day, 'month': time.month, 'year': time.year}
        # next_month if calculated first as next_day depends on
        # it. Also if next_month is different than time.month the
        # function will set up the rest of the fields
        try:
            self.__next_month(time.month, sol) and 
            self.__next_day(time.day, sol) and 
            self.__next_hour(time.hour, sol) and 
            self.__next_minute(time.minute, sol)
            return datetime.datetime(sol['year'], sol['month'], sol['day'], sol['hour'], sol['minute'])
        except:
            try:
                return self.next_run(datetime.datetime(time.year, time.month + 1, 1, 0, 0))
            except:
                return self.next_run(datetime.datetime(time.year + 1, 1, 1, 0, 0))

测试代码如下：

　　　　

from datetime import datetime

from crontab_parser import SimpleCrontabEntry
cron = SimpleCrontabEntry('03 */2 * * *')
datetime_time = datetime.now()
for page in range(10):
    datetime_time = cron.next_run(datetime_time)
    print "print",datetime_time

　　

输入结果如下：

　　

datetime_time 2021-03-12 14:00:39.545000
2021-03-12 14:03:00
2021-03-12 16:03:00
2021-03-12 18:03:00
2021-03-12 20:03:00
2021-03-12 22:03:00
2021-03-13 00:03:00
2021-03-13 02:03:00
2021-03-13 04:03:00
2021-03-13 06:03:00
2021-03-13 08:03:00

　　

计算crontab有什么作用，用处大了去了