'...' in time(...) 在python的timedate类中是什么意思？

Question

I am new to python programming.I am learning datetime module. But,going further,I saw:

from datetime import datetime
t = datetime.time()
print ("The current time is ", t)

But,I got error as:

TypeError                                 Traceback (most recent call last)
<ipython-input-109-91a2f569ccbd> in <module>
      8 #print(type(datetime.time()))
      9 # Get the current time
---> 10 t = datetime.time()
     11 
     12 print ("The current time is ", t)

TypeError: descriptor 'time' of 'datetime.datetime' object needs an argument

so I tried to see the help for datetime in my juypter notebook:

class datetime(date)
 |  datetime(year, month, day[, hour[, minute[, second[, microsecond[,tzinfo]]]]])
 |  
 |  The year, month and day arguments are required. tzinfo may be None, or an
 |  instance of a tzinfo subclass. The remaining arguments may be ints.
 |  
 |  Method resolution order:
 |      datetime
 |      date
 |      builtins.object
 |  
 |  Methods defined here:
 |  
 |  
 |  time(...)
 |      Return time object with same time but with tzinfo=None.
 |  
 |  
 |  now(tz=None) from builtins.type
 |      Returns new datetime object representing current time local to tz.
 |      
 |        tz
 |          Timezone object.
 |      
 |      If no tz is specified, uses local timezone.
 | 

I saw the class datetime has function time. As given by juypter notebook:

time(...)
 |      Return time object with same time but with tzinfo=None.

(I have not posted all functions above).I get confuse what the function parameter is expecting? I am unclear about these three dots.What does this three dots means?

So,I moved to python docs and https://docs.python.org/3/library/datetime.html#datetime.datetime.year .

And I saw,

datetime.time()
Return time object with same hour, minute, second, microsecond and fold. tzinfo is None. See also method timetz().

Changed in version 3.6: The fold value is copied to the returned time object.  

So,in this docs, i am seeing time() function has no any argument it is expecting.I again get confuse at this point.Since,error says that it expects at least a argument ,but in docs it is showing me the function is not expecting any argument . Can some one clarify me how can I see from juypter notebook what the function is expecting?

Answer 1

In your code you are trying to get the time from the time object directly, so you need to do:

from datetime import datetime
t = datetime.now().time()
print ("The current time is ", t)

# The current time is  18:11:56.271907

The class method datetime.now() is described here

Return the current local date and time. If optional argument tz is None or not specified, this is like today(), but, if possible, supplies more precision than can be gotten from going through a time.time() timestamp (for example, this may be possible on platforms supplying the C gettimeofday() function).

If you want to use the function time() directly you need to change your import:

import datetime
print(datetime.time())

# datetime.time(0, 0)

The import from datetime import datetime means that you are importing the object datetime from the module datetime, into this object you have the nested object time <method 'time' of 'datetime.datetime' objects> .

The datetime module is probably particularly confusing because the module also includes a datetime class, so datetime.datetime refers to the datetime class within the datetime module. If you do from datetime import datetime , you're only importing the datetime class, so when you refer to datetime in your code, it's referring to the datetime class, not the whole datetime module.

Using the import import datetime you are importing the module directly, where is located the function time() that use the class <class 'datetime.time'>

Reference to the time class is here

An idealized time, independent of any particular day, assuming that every day has exactly 24 60 60 seconds (there is no notion of “leap seconds” here). Attributes: hour, minute, second, microsecond, and tzinfo.

Reference to the datetime class nested into the datetime module is here

A combination of a date and a time. Attributes: year, month, day, hour, minute, second, microsecond, and tzinfo.

Inside this reference you can find the datetime.time() instance method

Return time object with same hour, minute, second, microsecond and fold. tzinfo is None. See also method timetz().

Answer 2

I get confuse what the function parameter is expecting? I am unclear about these three dots.What does this three dots means?

It means that the help function was unable to determine the actual arguments. The documentation is here ; the method does not expect any arguments. (Yes, it's hard to search the page because there are not enough page anchors and way too many times that the words "date" and "time" appear; sorry about that.)

The reason datetime.time() in your code does not work is that you are incorrectly trying to call an instance method as a class method. This does not make sense; you need to have an actual thing that represents a date and time, in order to pull the time out of it. If you want to know what time it is now, you create the date-and-time-representing-thing that represents "now", and get the time from that . Thus: datetime.now().time() . Here, now is a class method that asks the datetime class to create an instance representing "now".

Answer 3

If you only want to get the actual time then you can simply use:

from datetime import datetime

def test_time():

    date = datetime.now()
    time = datetime.time(date)

    print("This is the actual time", time)

datetime.now() gives you the actual date and time combined. At this point an instance of the datetime class was created. Then you can pass this date-Object to the time function, which simply returns the actual time.

Also the signature of the datetime-class shows you, that you have to pass parameters, when you want to instantiate the class. So if you want to create your own date, you can simply do it in the following way:

from datetime import datetime

def test_time():

    date = datetime(year=2020, month=8, day=31, hour=0, minute=0, second=0, microsecond=0)

    print("This is the actual date and time", date)