1, Introduction to datetime module

(1) The datetime module contains the following classes:

(2) , constants contained in the datetime module

2, date class

(1) , date object composition

1. The date object consists of year, month and day

date(year，month，day)

2. The data descriptors of year, month and day can be accessed:

>>> a = datetime.date.today()
>>> a
datetime.date(2017, 3, 22)
>>> a.year
2017
>>> a.month
3
>>> a.day
22 

3. Of course, you can also get the above values using the \\\\\\\\

>>> a.__getattribute__('year')
2017
>>> a.__getattribute__('month')
3
>>> a.__getattribute__('day')
22

(2) Methods and properties contained in, date objects

1, Method for date comparison size

The return value of the above method is True\False
An example is as follows:

>>> a=datetime.date(2017,3,1)
>>> b=datetime.date(2017,3,15)
>>> a.__eq__(b)
False
>>> a.__ge__(b)
False
>>> a.__gt__(b)
False
>>> a.__le__(b)
True
>>> a.__lt__(b)
True
>>> a.__ne__(b)
True

2. How many days is the difference between two dates

In fact, there is not much difference between the two methods, one is forward operation, the other is reverse operation

An example is as follows:

>>> a
datetime.date(2017, 3, 22)
>>> b
datetime.date(2017, 3, 15)
>>> a.__sub__(b)
datetime.timedelta(7)
>>> a.__rsub__(b)
datetime.timedelta(-7)

The return value type of the calculation result is datetime.timedelta. If you get the result of integer type, you can operate as follows:

>>> a.__sub__(b).days
7
>>> a.__rsub__(b).days
-7

3. ISO standardization date

If you want to use a date that conforms to ISO standards, use the following three methods:
1) . * isocalendar(...) *: returns a tuple containing three values: year year, week number week, weekday week (Monday is 1 7 on Sunday):
Examples are as follows

>>> a = datetime.date(2017,3,22)
>>> a.isocalendar()
(2017, 12, 3)
>>> a.isocalendar()[0]
2017
>>> a.isocalendar()[1]
12
>>> a.isocalendar()[2]
3


2). isoformat(...): returns a date string conforming to ISO 8601 standard (YYYY-MM-DD); 

>>> a = datetime.date(2017,3,22)
>>> a.isoformat()
'2017-03-22'

3) . isoweekday(...): returns the number of weeks (Monday is 1) of a specified date that conforms to ISO standards 7 on Sunday)
An example is as follows:

>>> a = datetime.date(2017,3,22)
>>> a.isoweekday()
3

4) Similar to isoweekday(...), there is also a weekday(...) method, except that the weekday(...) method returns 0 on Monday and 6 on Sunday
An example is as follows:

>>> a = datetime.date(2017,3,22)
>>> a.weekday()
2

4. Other methods and properties

1) . timetuple(...): in order to be compatible with time.localtime(...), this method returns an array of type time.struct_time, but some element values related to time are 0:

>>> a = datetime.date(2017,3,22)
>>> a.timetuple()
time.struct_time(tm_year=2017, tm_mon=3, tm_mday=22, tm_hour=0, tm_min=0, tm_sec=0, tm_wday=2, tm_yday=81, tm_isdst=-1)
>>> a.timetuple().tm_year
2017
>>> a.timetuple().tm_mon
3
>>> a.timetuple().tm_mday
22

2) . toolbar (...): returns the number of days from the beginning of the Gregorian calendar to the present. January 1, A.D. 1

>>> a = datetime.date(2017,3,22)
>>> a.toordinal()
736410

3) . replace(...): returns a new date object that replaces the specified date field. The three optional parameters are year, month and day. Note that the replacement is to generate a new object without affecting the original date object.

>>> a = datetime.date(2017,3,22)
>>> b = a.replace(2017,2,28)
>>> a
datetime.date(2017, 3, 22)
>>> b
datetime.date(2017, 2, 28)

4) The. Resolution: Date object represents the minimum unit of date. This is the day.

>>> datetime.date.resolution
datetime.timedelta(1)

5).fromordinal(...): convert Gregorian Calendar time to date object; Gregorian Calendar: a calendar representation method, similar to Chinese lunar calendar, which is widely used in western countries.

>>> a = datetime.date(2017,3,22)
>>> b = a.toordinal()
>>> datetime.date.fromordinal(b)
datetime.date(2017, 3, 22)

6).fromtimestamp(...): returns a date object based on the given time kill

>>> time.time()
1490165087.2242179
>>> datetime.date.fromtimestamp(time.time())
datetime.date(2017, 3, 22)

7).today(...): returns the current date

>>> datetime.date.today()
datetime.date(2017, 3, 22)

8).max: the maximum number of years, months, and days that the date class can represent

>>> datetime.date.max
datetime.date(9999, 12, 31)

9).min: the minimum number of years, months, and days that the date class can represent

>>> datetime.date.min
datetime.date(1, 1, 1)

(3) String output of,, date

1. If you want to convert a date object to a string object, you can use the \

>>> a = datetime.date(2017,3,22)
>>> a.__format__('%Y-%m-%d')
'2017-03-22'
>>> a.__format__('%Y/%m/%d')
'2017/03/22'
>>> a.__format__('%y/%m/%d')
'17/03/22'
>>> a.__format__('%D')
'03/22/17'

The equivalent method to this method is strftime(...)

>>> a.strftime("%Y%m%d")
'20170322'

For information about formatting strings, please refer to the last: appendix: time and date formatting symbols in python
2. If it's just a simple str ing to get the date, use the

>>> a.__str__()
'2017-03-22'

3. If you want to get the format of the ctime style, use ctime(...):

>>> a.ctime()
'Wed Mar 22 00:00:00 2017'

3, time class

(1) , data composition of time class

The time class consists of five parts: hour hour, minute, second second, microsecond and tzinfo

 time([hour[, minute[, second[, microsecond[, tzinfo]]]]])

Accordingly, there are five variables in the time class to store the corresponding values:

>>> a = datetime.time(12,20,59,899)
>>> a
datetime.time(12, 20, 59, 899)
>>> a.hour
12
>>> a.minute
20
>>> a.second
59
>>> a.microsecond
899
>>> a.tzinfo

Like the date class, the time class also contains the getattribute method to read related attributes:

>>> a.__getattribute__('hour')
12
>>> a.__getattribute__('minute')
20
>>> a.__getattribute__('second')
59

(2) , methods and properties in the time class

1. Compare time size

Related methods include: eq, ge, gt, le, lt, ne
The method here is the same as the method defined in the date class. The use method is the same as that of the date class. It is just introduced here. The example is as follows:

>>> a = datetime.time(12,20,59,899)
>>> b = datetime.time(11,20,59,889)
>>> a.__eq__(b)
False
>>> a.__ne__(b)
True
>>> a.__ge__(b)
True
>>> a.__gt__(b)
True
>>> a.__le__(b)
False
>>> a.__lt__(b)
False

2,__nonzero__(...)

Judge whether the time object is non-zero, and the return value is True/False:

>>> a = datetime.time(12,20,59,899)
>>> a.__nonzero__()
True

3. Other properties

1) , max: maximum schedule value:

>>> datetime.time.max
datetime.time(23, 59, 59, 999999)

2) min: minimum schedule indicator value

>>> datetime.time.min
datetime.time(0, 0)

3) , resolution: time interval unit is minute

>>> datetime.time.resolution
datetime.timedelta(0, 0, 1)

(3) , string output of time

1. If you want to convert a time object to a string object, you can use the \

>>> a = datetime.time(12,20,59,899)
>>> a.__format__('%H:%M:%S')
'12:20:59'

The equivalent method to this method is strftime(...)

>>> a = datetime.time(12,20,59,899)
>>> a.strftime('%H:%M:%S')
'12:20:59'

For information about formatting strings, please refer to the last: appendix: time and date formatting symbols in python
2. ISO standard output
If you want the output time character to conform to ISO standards, use isoformat(...):

>>> a = datetime.time(12,20,59,899)
>>> a.isoformat()
'12:20:59.000899'

3. If it's just a simple str ing to get the time, use \

>>> a = datetime.time(12,20,59,899)
>>> a.__str__()
'12:20:59.000899'

4, datetime class

(1) Data composition of datetime class

The date time class is actually a combination of the date class and the time class. Most of its methods and properties are inherited from these two classes. For related operation methods, please refer to the introduction of the two classes above. Its data structure is also composed of all the attributes of these two classes.

 datetime(year, month, day[, hour[, minute[, second[, microsecond[,tzinfo]]]]])

(2) , methods and properties specific to datetime

1, date(… ): returns the date part of the datetime object:

>>> a = datetime.datetime.now()
>>> a
datetime.datetime(2017, 3, 22, 16, 9, 33, 494248)
>>> a.date()
datetime.date(2017, 3, 22)

2, time(... ): returns the time part of the datetime object:

>>> a = datetime.datetime.now()
>>> a
datetime.datetime(2017, 3, 22, 16, 9, 33, 494248)
>>> a.time()
datetime.time(16, 9, 33, 494248)

3,utctimetuple(… ): return UTC time tuple:

>>> a = datetime.datetime.now()
>>> a
datetime.datetime(2017, 3, 22, 16, 9, 33, 494248)
>>> a.utctimetuple()
time.struct_time(tm_year=2017, tm_mon=3, tm_mday=22, tm_hour=16, tm_min=9, tm_sec=33, tm_wday=2, tm_yday=81, tm_isdst=0)

4,combine(… ): merge a date object and a time object to generate a datetime object:

>>> a = datetime.datetime.now()
>>> a
datetime.datetime(2017, 3, 22, 16, 9, 33, 494248)
>>>datetime.datetime.combine(a.date(),a.time())
datetime.datetime(2017, 3, 22, 16, 9, 33, 494248)

5, now(... ): returns the datetime object of the current datetime:

>>> a = datetime.datetime.now()
>>> a
datetime.datetime(2017, 3, 22, 16, 9, 33, 

6,utcnow(… ): returns the UTC datetime object for the current datetime:

>>> a = datetime.datetime.utcnow()
>>> a
datetime.datetime(2017, 3, 22, 8, 26, 54, 935242)

7,strptime(… ): return a corresponding datetime object according to the two parameters of string and format:

>>> datetime.datetime.strptime('2017-3-22 15:25','%Y-%m-%d %H:%M')
datetime.datetime(2017, 3, 22, 15, 25)

8,utcfromtimestamp(… ): datetime object of UTC timestamp with timestamp value of time.time():

>>> datetime.datetime.utcfromtimestamp(time.time())
datetime.datetime(2017, 3, 22, 8, 29, 7, 654272)

5, timedelta class

The timedelta class is used to calculate the difference between two datetime objects.  
This class contains the following properties:
1. Days: days
2. Microseconds: microseconds (> = 0 and < 1 second)
3. Seconds: seconds (> = 0 and < 1 day)

6, Date calculation practice

1. Get the current date and time:

>>> now = datetime.datetime.now()
>>> now
datetime.datetime(2017, 3, 22, 16, 55, 49, 148233)
>>> today = datetime.date.today()
>>> today
datetime.date(2017, 3, 22)
>>> now.date()
datetime.date(2017, 3, 22)
>>> now.time()
datetime.time(16, 55, 49, 148233)

2. Get the date of the first and last day of last month:

>>> today = datetime.date.today()
>>> today
datetime.date(2017, 3, 22)
>>> mlast_day = datetime.date(today.year, today.month, 1) - datetime.timedelta(1)
>>> mlast_day
datetime.date(2017, 2, 28)
>>> mfirst_day = datetime.date(mlast_day.year, mlast_day.month, 1)
>>> mfirst_day
datetime.date(2017, 2, 1)

3. Acquisition time difference

Time difference in seconds

>>> start_time = datetime.datetime.now()
>>> end_time = datetime.datetime.now()
>>> (end_time - start_time).seconds
7

The difference can be viewed not only in seconds, but also in days, seconds and microseconds

4. Calculate the time 8 hours after the current time

>>> d1 = datetime.datetime.now()
>>> d2 = d1 + datetime.timedelta(hours = 8)
>>> d2
datetime.datetime(2017, 3, 23, 1, 10, 37, 182240)

Can be calculated: days, hours, minutes, seconds, microseconds

5. Calculate the date of last Monday and Sunday

today = datetime.date.today()
>>> today
datetime.date(2017, 3, 23)
>>> today_weekday = today.isoweekday()
>>> last_sunday = today - datetime.timedelta(days=today_weekday)
>>> last_monday = last_sunday - datetime.timedelta(days=6)
>>> last_sunday
datetime.date(2017, 3, 19)
>>> last_monday
datetime.date(2017, 3, 13)

6. Calculate the last day of the month and the number of days of the month

>>> date = datetime.date(2017,12,20)
>>> def eomonth(date_object):
...     if date_object.month == 12:
...         next_month_first_date = datetime.date(date_object.year+1,1,1)
...     else:
...         next_month_first_date = datetime.date(date_object.year, date_object.month+1, 1)
...     return next_month_first_date - datetime.timedelta(1)
...
>>> eomonth(date)
datetime.date(2017, 12, 31)
>>> eomonth(date).day
31

7. Calculate the day of the next month of the specified date

Here we call the function eomonth(...) in the previous item

>>> date = datetime.date(2017,12,20)                                            
>>> def edate(date_object):                                                     
...     if date_object.month == 12:                          
...         next_month_date = datetime.date(date_object.year+1, 1,date_object.day)
...     else:
...         next_month_first_day = datetime.date(date_object.year,date_object.month+1,1)
...         if date_object.day > eomonth(last_month_first_day).day:
...             next_month_date = datetime.date(date_object.year,date_object.month+1,eomonth(last_month_first_day).day)
...         else:
...             next_month_date = datetime.date(date_object.year, date_object.month+1, date_object.day)
...     return next_month_date
...
>>> edate(date)
datetime.date(2018, 1, 20)

8. Obtain the time period from Monday to today and the corresponding time period of last week

>>> today = datetime.date.today()
>>> this_monday = today - datetime.timedelta(today.isoweekday()-1)
>>> last_monday = this_monday - datetime.timedelta(7)
>>> last_weekday = today -datetime.timedelta(7)
>>> this_monday
datetime.date(2017, 3, 20)
>>> today
datetime.date(2017, 3, 23)
>>> last_monday
datetime.date(2017, 3, 13)
>>> last_weekday
datetime.date(2017, 3, 16)

Appendix: time and date format symbols in python: