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

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