Exploring Time
==============

Background
----------

The motivating question -- *how do you translate strings to times?* There are two cases that I am going to look at:

   * Relative Time: a specification of hours, minutes, seconds, etc.
   * Absolute Time: a unique moment (e.g. '10-24-2013 9:14 pm')

The reason for looking at this is to find a way or ways to translate a configuration file to time-specifications for running code. Some possible uses:

   * Finding an execution-time for a command such as `iperf`
   * Finding a stopping time when the code shouldn't go past
   * Finding a starting time when code should be run



.. exploring-time-relative:
Relative Time
-------------

This seems to be the easier case. Say we have a specification of the form::

   run_time = 1 hour 20 minutes

For certain cases it would make sense to convert it to an integer or float so you could pass it to a command (like `time.sleep`) in other cases it might make sense to convert it to a timedelta so you can compare it to a specific time (like `datetime.now`). In any case, the first step would seem to be to tokenize the string to get the times. Since the configuration for this package largely passes through ConfigParse, I am going to assume that only strings with only the time information will be handled (i.e. 'run_time =' won't be in the string gotten from the example specification given above).

First, I'll set up some regular expressions to tokenize the strings.

::

    DIGIT = r'\d'
    ONE_OR_MORE = r"+"
    ZERO_OR_MORE = r'*'
    DECIMAL = r'\.'
    SPACE = r'\s'
    SPACES = SPACE + ONE_OR_MORE
    OPTIONAL_SPACES = SPACE + ZERO_OR_MORE
    OR = r'|'
    
    # groups
    NAMED = "(?P<{n}>{e})"
    GROUPED = "({0})"
    
    # numbers
    INTEGER = DIGIT + ONE_OR_MORE
    FLOAT = INTEGER + DECIMAL + INTEGER
    
    REAL = INTEGER + OR + FLOAT
    
    WEEKS = NAMED.format(n='weeks', e=REAL) + OPTIONAL_SPACES + '[wW]'
    DAYS = NAMED.format(n='days', e=REAL) + OPTIONAL_SPACES + '[dD]'
    
    # compiled_expressions
    DAY_EXPRESSION = re.compile(DAYS)
    WEEK_EXPRESSION = re.compile(WEEKS)
    

::

    example_1 = '2 days 3 hours 10 Weeks'
    example_2 =  '1.2Weeks 6.2 days'
    
    match = DAY_EXPRESSION.search(example_1)
    print "Days: " + match.group('days')
    
    match = DAY_EXPRESSION.search(example_2)
    print 'Days: ' + match.group('days')
    

::

    Days: 2
    Days: 6.2
    

::

    match = WEEK_EXPRESSION.search(example_1)
    print 'weeks: ' + match.group('weeks')
    match = WEEK_EXPRESSION.search(example_2)
    print 'Weeks: ' + match.group('weeks')
    

::

    weeks: 10
    Weeks: 1.2