Python | How to time the program

This article aims to show how to calculate the time it takes to perform various tasks. 
A simple solution to it is to use time module. This module contains various time-related functions. Also it’s very useful to put a higher-level interface over these functions and use them as a stop-watch as explained in the code below – 

Code #1 : 

Python3

# Using time module
import time

# defining the class
class Timer:

def __init__(self, func = time.perf_counter):
    self.elapsed = 0.0
    self._func = func
    self._start = None

# starting the module
def start(self):
    if self._start is not None:
        raise RuntimeError('Already started')
    self._start = self._func()

# stopping the timer
def stop(self):
    if self._start is None:
        raise RuntimeError('Not started')
    end = self._func()
    self.elapsed += end - self._start
    self._start = None

# resetting the timer
def reset(self):
    self.elapsed = 0.0
    @property

def running(self):
    return self._start is not None

def __enter__(self):
    self.start()
    return self

def __exit__(self, *args):
    self.stop()

We can start, stopped or reset this timer using this class as needed by the user so as to keep a track of the total elapsed time in the elapsed attribute. To do so, it is mentioned in the code below – 

Code #2 :

Python3

# using the class Timer()
def countdown(n):
    while n > 0:
        n -= 1

# Use 1: Explicit start / stop
time = Timer()

# start
time.start()
countdown(1000000)

# stop
time.stop()
print(time.elapsed)

# Use 2: As a context manager
with time:
    countdown(1000000)

print(time.elapsed)

with Timer() as t2:
    countdown(1000000)

print(t2.elapsed)

• The code above gives a very simple but still very useful class for measuring the time and tracking elapsed time. 
  It also illustrated how to support contextmanagement protocol and the with statement.
• The underlying time function is a concern while performing the time functions. As the accuracy of timing measurements made with functions such as time.time() or time.clock() varies according to the operating system.
• The highest-resolution timer available on the system in contrast is used by time.perf_counter().

To amount the CPU time used by process, time.process_time() is used instead as explained in the code below: 

Code #3 : 

Python3

t = Timer(time.process_time)
with t:
    countdown(1000000)
print(t.elapsed)

Both the time.perf_counter() and time.process_time() return a “time” in fractional seconds. To make sense of the results, call the functions twice and compute a time difference as the actual value of the time doesn’t have any particular meaning.