Pythonic way to Validate time input (only for Hr, Min, Sec)

Question

In my application,I am getting time input in a variable in string format e.g. Values = '12,12,12'.

Now i need to validate it h<24 M<60 S<60 etc. and i want final output in '%H:%M:%S' format.
To get this i tried datetime.time().

I had 1st tried with values = '12' then '12,12,12'.

In [1]: import datetime

In [2]: values = '12'

In [3]: d = datetime.time(values)

TypeError  Traceback (most recent call last)
/mypc/test/<ipython console> in <module>()
TypeError: an integer is required

In [4]: d = datetime.time(int(values))

In [5]: d
Out[5]: datetime.time(12, 0)

In [6]: d.strftime('%H:%M:%S')
Out[6]: '12:00:00'

In [7]: s = d.strftime('%H:%M:%S')

In [8]: s
Out[8]: '12:00:00'

In [9]: values = '12,12,12'

In [10]: d = datetime.time(int(values))

ValueError: invalid literal for int() with base 10: '12,12,12'

But it works as below.

In [24]: datetime.time(12,12,12).strftime('%H:%M:%S')
Out[24]: '12:12:12'

So problem is that datetime.time() is taking input as integer and '12,12,12' string cannot be converted in int.

Is there any other way(otherthan regexp) to do the validation for only Hr:M:S.

Answer 1

You have to unpack the values:

>>> values = '12,12,12'
>>> values = ast.literal_eval(values)
>>> datetime.time(*values)
datetime.time(12, 12, 12)

This last statement will raise an error if the time given is invalid.

To avoid problems with zero-padded numbers, as "wim" pointed, it's possible to change the second line to:

values = (int(i) for i in values.split(','))

or

values = map(int, values.split(','))

Answer 2

Please note that the counterpart of strftime is strptime, that is, if you need to parse a time you can use strptime using a format string the same way as you use strftime to print a time using that format string:

>>> import time
>>> t = time.strptime('12,12,12', '%H,%M,%S')
>>> time.strftime('%H:%M:%S', t)
'12:12:12'

This way, strptime takes care of the validation (H<24, M<60, S<=61):

>>> time.strptime('24,0,0', '%H,%M,%S')
...
ValueError: time data '24,0,0' does not match format '%H,%M,%S'
>>> time.strptime('0,60,0', '%H,%M,%S')
...
ValueError: time data '0,60,0' does not match format '%H,%M,%S'
>>> time.strptime('0,0,62', '%H,%M,%S')
...
ValueError: unconverted data remains: 2

Note that strptime allows S<=61 as explained in the documentation:

The range really is 0 to 61; this accounts for leap seconds and the (very rare) double leap seconds.

If that's a problem for you, then you probably need to parse that value in your code.