How should a clock object be made in Python?

Question

I'm making a very simple clock object in Python. I want to be able to instantiate a clock giving it a name and have it record the time it is running for, with pause functionality. I think I've nearly got it, but the pause functionality is giving me some trouble -- the clock continues to accumulate time even when stopped. I think the problem lies in the way the accumulated run time (the _runTime data attribute) is updated (in the method update()). I would welcome assistance in getting this code working sensibly and would welcome any other comments on making the ideas here better.

import time
import datetime

def style_datetime_object(
    datetimeObject = None,
    style = "YYYY-MM-DDTHHMMSS"
    ):
    # filename safe
    if style == "YYYY-MM-DDTHHMMSSZ":
        return(datetimeObject.strftime('%Y-%m-%dT%H%M%SZ'))
    # microseconds
    elif style == "YYYY-MM-DDTHHMMSSMMMMMMZ":
        return(datetimeObject.strftime('%Y-%m-%dT%H%M%S%fZ'))
    # elegant
    elif style == "YYYY-MM-DD HH:MM:SS UTC":
        return(datetimeObject.strftime('%Y-%m-%d %H:%M:%SZ'))
    # UNIX time in seconds with second fraction
    elif style == "UNIX time S.SSSSSS":
        return((datetimeObject - datetime.datetime.utcfromtimestamp(0)).total_seconds())
    # UNIX time in seconds rounded
    elif style == "UNIX time S":
        return(int((datetimeObject - datetime.datetime.utcfromtimestamp(0)).total_seconds()))
    # filename safe
    else:
        return(datetimeObject.strftime('%Y-%m-%dT%H%M%SZ'))

class Clock(object):

    def __init__(
        self,
        name  = None,
        start = True
        ):
        # options
        self._name      = name
        self._start     = start # Boolean start clock on instantiation
        # internal
        self._startTime = None
        self._stopTime  = None
        self._runTime   = None
        self._running   = False
        # If a global clock list is detected, add a clock instance to it.
        if "clocks" in globals():
            clocks.add(self)
        if self._start:
            self.start()

    def name(
        self
        ):
        return(self._name)

    def start(
        self
        ):
        self._running   = True
        self._startTime = datetime.datetime.utcnow()

    def stop(
        self
        ):
        self._stopTime = datetime.datetime.utcnow()
        self._running  = False
        self.update()

    def startTime(
        self
        ):
        return(style_datetime_object(datetimeObject = self._startTime))

    def update(
        self
        ):
        # If the clock is running, the run time is the difference between the
        # current time and the start time (added to any previously accumulated
        # run time). If the clock is not running, the run time is the difference
        # between the stop time and the start time (added to any previously
        # accumulated run time).
        if self._running:
            if self._runTime:
                self._runTime = self._runTime + datetime.datetime.utcnow() - self._startTime
            else:
                self._runTime = datetime.datetime.utcnow() - self._startTime
        else:
            if self._runTime:
                self._runTime = self._runTime + self._stopTime - self._startTime
            else:
                self._runTime = self._stopTime - self._startTime

    def time(
        self
        ):
        self.update()
        return(self._runTime.total_seconds())

print("create clock")
a = Clock(name = "hello")
print("clock start time: {time}".format(time = a.startTime()))
print("sleep 2 seconds")
time.sleep(2)
print("clock current time (s): {time}".format(time = a.time()))

print

print("create new clock")
b = Clock(name = "world")
print("clock start time: {time}".format(time = b.startTime()))
print("sleep 2 seconds")
time.sleep(2)
print("clock current time (s): {time}".format(time = b.time()))
print("stop clock")
b.stop()
print("sleep 2 seconds")
time.sleep(2)
print("clock current time (s): {time}".format(time = b.time()))

Sorry - the clock continues accumulating time when it shouldn't. The pause should stop it from accumulating time. I think the problem lies in the way the _runTime data attribute gets updated in the update() method. — d3pd
– d3pd, Commented Dec 10, 2014 at 21:54

Paulo Scardine · Accepted Answer · 2014-12-10 23:05:45Z

I found your code hard to follow. Here is my (much smaller) clock anyway, may be you can draw some inspiration to implement any lacking feature later.

import datetime

class Clock(object):
    def __init__(self):
        self.reset()
    def reset(self):
        self.accumulator = datetime.timedelta(0)
        self.started = None
    def start_stop(self):
        if self.started:
            self.accumulator += (
                datetime.datetime.utcnow() - self.started
            )
            self.started = None
        else:
            self.started = datetime.datetime.utcnow()
    @property
    def elapsed(self):
        if self.started:
            return self.accumulator + (
                datetime.datetime.utcnow() - self.started
            )
        return self.accumulator
    def __repr__(self):
        return "<Clock {} ({})>".format(
            self.elapsed,
            'started' if self.started else 'stopped'
        )

Tests:

c = Clock()
print c
print "Starting..."; c.start_stop()
for i in range(4):
    time.sleep(2)
    print c
print "Stopping..."; c.start_stop()
for i in range(4):
    time.sleep(2)
    print c
print "Starting..."; c.start_stop()
for i in range(4):
    time.sleep(2)
    print c
print "Resetting..."; c.reset()
print c

Result:

<Clock 0:00:00 (stopped)>
Starting...
<Clock 0:00:02.002085 (started)>
<Clock 0:00:04.004263 (started)>
<Clock 0:00:06.006483 (started)>
<Clock 0:00:08.007675 (started)>
Stopping...
<Clock 0:00:08.007756 (stopped)>
<Clock 0:00:08.007756 (stopped)>
<Clock 0:00:08.007756 (stopped)>
<Clock 0:00:08.007756 (stopped)>
Starting...
<Clock 0:00:10.009876 (started)>
<Clock 0:00:12.012034 (started)>
<Clock 0:00:14.013143 (started)>
<Clock 0:00:16.015291 (started)>
Resetting...
<Clock 0:00:00 (stopped)>

Thanks for your help on that! Your toggling method was particularly clear.

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