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How do I get my program to sleep for 50 milliseconds?
(6 answers)
Closed 3 years ago.
How do I put a time delay in a Python script?
This delays for 2.5 seconds:
import time
time.sleep(2.5)
Here is another example where something is run approximately once a minute:
import time
while True:
print("This prints once a minute.")
time.sleep(60) # Delay for 1 minute (60 seconds).
Use sleep() from the time module. It can take a float argument for sub-second resolution.
from time import sleep
sleep(0.1) # Time in seconds
How can I make a time delay in Python?
In a single thread I suggest the sleep function:
>>> from time import sleep
>>> sleep(4)
This function actually suspends the processing of the thread in which it is called by the operating system, allowing other threads and processes to execute while it sleeps.
Use it for that purpose, or simply to delay a function from executing. For example:
>>> def party_time():
... print('hooray!')
...
>>> sleep(3); party_time()
hooray!
"hooray!" is printed 3 seconds after I hit Enter.
Example using sleep with multiple threads and processes
Again, sleep suspends your thread - it uses next to zero processing power.
To demonstrate, create a script like this (I first attempted this in an interactive Python 3.5 shell, but sub-processes can't find the party_later function for some reason):
from concurrent.futures import ThreadPoolExecutor, ProcessPoolExecutor, as_completed
from time import sleep, time
def party_later(kind='', n=''):
sleep(3)
return kind + n + ' party time!: ' + __name__
def main():
with ProcessPoolExecutor() as proc_executor:
with ThreadPoolExecutor() as thread_executor:
start_time = time()
proc_future1 = proc_executor.submit(party_later, kind='proc', n='1')
proc_future2 = proc_executor.submit(party_later, kind='proc', n='2')
thread_future1 = thread_executor.submit(party_later, kind='thread', n='1')
thread_future2 = thread_executor.submit(party_later, kind='thread', n='2')
for f in as_completed([
proc_future1, proc_future2, thread_future1, thread_future2,]):
print(f.result())
end_time = time()
print('total time to execute four 3-sec functions:', end_time - start_time)
if __name__ == '__main__':
main()
Example output from this script:
thread1 party time!: __main__
thread2 party time!: __main__
proc1 party time!: __mp_main__
proc2 party time!: __mp_main__
total time to execute four 3-sec functions: 3.4519670009613037
Multithreading
You can trigger a function to be called at a later time in a separate thread with the Timer threading object:
>>> from threading import Timer
>>> t = Timer(3, party_time, args=None, kwargs=None)
>>> t.start()
>>>
>>> hooray!
>>>
The blank line illustrates that the function printed to my standard output, and I had to hit Enter to ensure I was on a prompt.
The upside of this method is that while the Timer thread was waiting, I was able to do other things, in this case, hitting Enter one time - before the function executed (see the first empty prompt).
There isn't a respective object in the multiprocessing library. You can create one, but it probably doesn't exist for a reason. A sub-thread makes a lot more sense for a simple timer than a whole new subprocess.
Delays can be also implemented by using the following methods.
The first method:
import time
time.sleep(5) # Delay for 5 seconds.
The second method to delay would be using the implicit wait method:
driver.implicitly_wait(5)
The third method is more useful when you have to wait until a particular action is completed or until an element is found:
self.wait.until(EC.presence_of_element_located((By.ID, 'UserName'))
There are five methods which I know: time.sleep(), pygame.time.wait(), matplotlib's pyplot.pause(), .after(), and asyncio.sleep().
time.sleep() example (do not use if using tkinter):
import time
print('Hello')
time.sleep(5) # Number of seconds
print('Bye')
pygame.time.wait() example (not recommended if you are not using the pygame window, but you could exit the window instantly):
import pygame
# If you are going to use the time module
# don't do "from pygame import *"
pygame.init()
print('Hello')
pygame.time.wait(5000) # Milliseconds
print('Bye')
matplotlib's function pyplot.pause() example (not recommended if you are not using the graph, but you could exit the graph instantly):
import matplotlib
print('Hello')
matplotlib.pyplot.pause(5) # Seconds
print('Bye')
The .after() method (best with Tkinter):
import tkinter as tk # Tkinter for Python 2
root = tk.Tk()
print('Hello')
def ohhi():
print('Oh, hi!')
root.after(5000, ohhi) # Milliseconds and then a function
print('Bye')
Finally, the asyncio.sleep() method (has to be in an async loop):
await asyncio.sleep(5)
A bit of fun with a sleepy generator.
The question is about time delay. It can be fixed time, but in some cases we might need a delay measured since last time. Here is one possible solution:
Delay measured since last time (waking up regularly)
The situation can be, we want to do something as regularly as possible and we do not want to bother with all the last_time, next_time stuff all around our code.
Buzzer generator
The following code (sleepy.py) defines a buzzergen generator:
import time
from itertools import count
def buzzergen(period):
nexttime = time.time() + period
for i in count():
now = time.time()
tosleep = nexttime - now
if tosleep > 0:
time.sleep(tosleep)
nexttime += period
else:
nexttime = now + period
yield i, nexttime
Invoking regular buzzergen
from sleepy import buzzergen
import time
buzzer = buzzergen(3) # Planning to wake up each 3 seconds
print time.time()
buzzer.next()
print time.time()
time.sleep(2)
buzzer.next()
print time.time()
time.sleep(5) # Sleeping a bit longer than usually
buzzer.next()
print time.time()
buzzer.next()
print time.time()
And running it we see:
1400102636.46
1400102639.46
1400102642.46
1400102647.47
1400102650.47
We can also use it directly in a loop:
import random
for ring in buzzergen(3):
print "now", time.time()
print "ring", ring
time.sleep(random.choice([0, 2, 4, 6]))
And running it we might see:
now 1400102751.46
ring (0, 1400102754.461676)
now 1400102754.46
ring (1, 1400102757.461676)
now 1400102757.46
ring (2, 1400102760.461676)
now 1400102760.46
ring (3, 1400102763.461676)
now 1400102766.47
ring (4, 1400102769.47115)
now 1400102769.47
ring (5, 1400102772.47115)
now 1400102772.47
ring (6, 1400102775.47115)
now 1400102775.47
ring (7, 1400102778.47115)
As we see, this buzzer is not too rigid and allow us to catch up with regular sleepy intervals even if we oversleep and get out of regular schedule.
The Tkinter library in the Python standard library is an interactive tool which you can import. Basically, you can create buttons and boxes and popups and stuff that appear as windows which you manipulate with code.
If you use Tkinter, do not use time.sleep(), because it will muck up your program. This happened to me. Instead, use root.after() and replace the values for however many seconds, with a milliseconds. For example, time.sleep(1) is equivalent to root.after(1000) in Tkinter.
Otherwise, time.sleep(), which many answers have pointed out, which is the way to go.
Delays are done with the time library, specifically the time.sleep() function.
To just make it wait for a second:
from time import sleep
sleep(1)
This works because by doing:
from time import sleep
You extract the sleep function only from the time library, which means you can just call it with:
sleep(seconds)
Rather than having to type out
time.sleep()
Which is awkwardly long to type.
With this method, you wouldn't get access to the other features of the time library and you can't have a variable called sleep. But you could create a variable called time.
Doing from [library] import [function] (, [function2]) is great if you just want certain parts of a module.
You could equally do it as:
import time
time.sleep(1)
and you would have access to the other features of the time library like time.clock() as long as you type time.[function](), but you couldn't create the variable time because it would overwrite the import. A solution to this to do
import time as t
which would allow you to reference the time library as t, allowing you to do:
t.sleep()
This works on any library.
If you would like to put a time delay in a Python script:
Use time.sleep or Event().wait like this:
from threading import Event
from time import sleep
delay_in_sec = 2
# Use time.sleep like this
sleep(delay_in_sec) # Returns None
print(f'slept for {delay_in_sec} seconds')
# Or use Event().wait like this
Event().wait(delay_in_sec) # Returns False
print(f'waited for {delay_in_sec} seconds')
However, if you want to delay the execution of a function do this:
Use threading.Timer like this:
from threading import Timer
delay_in_sec = 2
def hello(delay_in_sec):
print(f'function called after {delay_in_sec} seconds')
t = Timer(delay_in_sec, hello, [delay_in_sec]) # Hello function will be called 2 seconds later with [delay_in_sec] as the *args parameter
t.start() # Returns None
print("Started")
Outputs:
Started
function called after 2 seconds
Why use the later approach?
It does not stop execution of the whole script (except for the function you pass it).
After starting the timer you can also stop it by doing timer_obj.cancel().
asyncio.sleep
Notice in recent Python versions (Python 3.4 or higher) you can use asyncio.sleep. It's related to asynchronous programming and asyncio. Check out next example:
import asyncio
from datetime import datetime
#asyncio.coroutine
def countdown(iteration_name, countdown_sec):
"""
Just count for some countdown_sec seconds and do nothing else
"""
while countdown_sec > 0:
print(f'{iteration_name} iterates: {countdown_sec} seconds')
yield from asyncio.sleep(1)
countdown_sec -= 1
loop = asyncio.get_event_loop()
tasks = [asyncio.ensure_future(countdown('First Count', 2)),
asyncio.ensure_future(countdown('Second Count', 3))]
start_time = datetime.utcnow()
# Run both methods. How much time will both run...?
loop.run_until_complete(asyncio.wait(tasks))
loop.close()
print(f'total running time: {datetime.utcnow() - start_time}')
We may think it will "sleep" for 2 seconds for first method and then 3 seconds in the second method, a total of 5 seconds running time of this code. But it will print:
total_running_time: 0:00:03.01286
It is recommended to read asyncio official documentation for more details.
While everyone else has suggested the de facto time module, I thought I'd share a different method using matplotlib's pyplot function, pause.
An example
from matplotlib import pyplot as plt
plt.pause(5) # Pauses the program for 5 seconds
Typically this is used to prevent the plot from disappearing as soon as it is plotted or to make crude animations.
This would save you an import if you already have matplotlib imported.
This is an easy example of a time delay:
import time
def delay(period='5'):
# If the user enters nothing, it'll wait 5 seconds
try:
# If the user not enters a int, I'll just return ''
time.sleep(period)
except:
return ''
Another, in Tkinter:
import tkinter
def tick():
pass
root = Tk()
delay = 100 # Time in milliseconds
root.after(delay, tick)
root.mainloop()
You also can try this:
import time
# The time now
start = time.time()
while time.time() - start < 10: # Run 1- seconds
pass
# Do the job
Now the shell will not crash or not react.
I have a CSV that I've loaded into Google Cloud Storage, and I am creating a Dataflow pipeline that will read and process the CSV, then perform a count of of listings by a single column.
How do I isolate the single column. Let's say the columns are id, city, sports_team. I want to count how many occurrences of a city show up.
My starting code is like so:
# Python's regular expression library
import re
# Beam and interactive Beam imports
import apache_beam as beam
from apache_beam.runners.interactive.interactive_runner import InteractiveRunner
import apache_beam.runners.interactive.interactive_beam as ib
class SplitRecords(beam.DoFn):
"""Spilt the element into records, return rideable_type record."""
def process(self, element):
records = element.split(",")
return [records[1]]
p = beam.Pipeline(InteractiveRunner())
lines = p | 'read in file' >> beam.io.ReadFromText("gs://ny-springml-data/AB_NYC_2019.csv", skip_header_lines=1)
records = lines | beam.ParDo(SplitRecords())
groups = (records | beam.Map(lambda x: (x, 1)) | beam.CombinePerKey(sum))
groups | beam.io.WriteToText('TEST2.txt')
I am getting an IndexError: list index out of range.... I'm extremely newb at all of this, so any help is appreciated.
Presumably there's some unexpected line in your CVS file, e.g. a blank one. You could do something like
if len(records) < 2:
raise ValueError("Bad line: %r" % element)
else:
yield records[1]
to get a better error message. I would also recommend looking into using Beam Dataframes for this kind of task.
I've created my first ever python script and it works fine in the foreground, but when I run it in the background it creates, but fails to write anything to the file. I run the script with command : python -u testit.py &
Please help me understand why this happens.
#!/usr/bin/env python
import time
import datetime
dt = datetime.datetime.now()
dtLog = dt.strftime("ThermoLogs/TempLOG%Y%m%d")
f = open(dtLog,"a")
while True:
dt = datetime.datetime.now()
print('{:%Y-%m-%d %H:%M:%S}'.format(dt))
f.write('{:%Y-%m-%d %H:%M:%S}'.format(dt))
f.write('\n')
time.sleep(5)
The output will arrive in bursts (it is being buffered). With the sleep set to 0.01 I am getting bursts about every 2 seconds. So for a delay of 5 you will get them much less frequent. You may also note that it outputs all pending outputs when you terminate it.
To make the output arrive now call f.flush().
I don't see any difference between foreground and background. However it should not buffer stdout when going to a terminal.
I am trying to put together some code in Python 3.6 to help test the computer hardware that passes through my hands as an IT tech.
I'd like to have a script that plays a simple sine wave tone on the left speaker, then the right and then the both speakers together.
I have found a potentially helpful script over at Pyaudio How to get sound on only one speaker but some of the code to actually run it is missing - chiefly the code for making sin wave tones. I have looked around online and have tried reverse-engineering this back into the code on that page but the maths is a little high-level for me! Sorry.
Thanks,
Will
Update:
I think I have found a partial (albeit long-winded solution) with 'sounddevice' for python 3
#!/usr/bin/env python3
import argparse
import logging
parser = argparse.ArgumentParser(description=__doc__)
parser.add_argument("filename", help="audio file to be played back")
parser.add_argument("-d", "--device", type=int, help="device ID")
args = parser.parse_args()
try:
import sounddevice as sd
import soundfile as sf
data, fs = sf.read(args.filename, dtype='float32')
sd.play(data, fs, device=args.device, blocking=True, mapping=[1])
status = sd.get_status()
if status:
logging.warning(str(status))
except BaseException as e:
# This avoids printing the traceback, especially if Ctrl-C is used.
raise SystemExit(str(e))
The main chunk of code is repeat twice more but with "mapping = [1]" changed to "mapping = [2]" to test the right speaker and finally with "mapping = [?]" removed in the final block to test both speakers.
I found this over at https://python-sounddevice.readthedocs.io/en/0.2.1/examples.html.
Of course, if anyone knows a quicker and graceful way of getting this done, please share!
You could generate the sine tone directly in Python instead of loading it from a file. I've written some tutorials about creating simple sine tones:
https://nbviewer.jupyter.org/github/mgeier/python-audio/blob/master/simple-signals.ipynb
http://nbviewer.jupyter.org/github/spatialaudio/communication-acoustics-exercises/blob/master/intro.ipynb
Those tutorials use NumPy, because it makes manipulating the audio buffers very easy. But you can of course also do it in pure Python, if you prefer.
Here's an example:
#!/usr/bin/env python3
import math
import sounddevice as sd
sd.default.device = None
sd.default.samplerate = samplerate = 48000
duration = 1.5
volume = 0.3
frequency = 440
# fade time in seconds:
fade_in = 0.01
fade_out = 0.3
buffer = memoryview(bytearray(int(duration * samplerate) * 4)).cast('f')
for i in range(len(buffer)):
buffer[i] = volume * math.cos(2 * math.pi * frequency * i / samplerate)
fade_in_samples = int(fade_in * samplerate)
for i in range(fade_in_samples):
buffer[i] *= i / fade_in_samples
fade_out_samples = int(fade_out * samplerate)
for i in range(fade_out_samples):
buffer[-(i + 1)] *= i / fade_out_samples
for mapping in ([1], [2], [1, 2]):
sd.play(buffer, blocking=True, mapping=mapping)
sd.sleep(500)
Note that this code is using 32-bit floating point numbers (each one using 4 bytes), that's why we reserve 4 times more bytes in our bytearray than the required number of samples.
On OS X 10.4/5/6:
I have a parent process which spawns a child. I want to kill the parent without killing the child. Is it possible? I can modify source on either app.
As NSD asked, it really depends on how it is spawned. If you are using a shell script, for example, you can use the nohup command to run the child through.
If you are using fork/exec, then it is a little more complicated, but no too much so.
From http://code.activestate.com/recipes/66012/
import sys, os
def main():
""" A demo daemon main routine, write a datestamp to
/tmp/daemon-log every 10 seconds.
"""
import time
f = open("/tmp/daemon-log", "w")
while 1:
f.write('%s\n' % time.ctime(time.time()))
f.flush()
time.sleep(10)
if __name__ == "__main__":
# do the UNIX double-fork magic, see Stevens' "Advanced
# Programming in the UNIX Environment" for details (ISBN 0201563177)
try:
pid = os.fork()
if pid > 0:
# exit first parent
sys.exit(0)
except OSError, e:
print >>sys.stderr, "fork #1 failed: %d (%s)" % (e.errno, e.strerror)
sys.exit(1)
# decouple from parent environment
os.chdir("/")
os.setsid()
os.umask(0)
# do second fork
try:
pid = os.fork()
if pid > 0:
# exit from second parent, print eventual PID before
print "Daemon PID %d" % pid
sys.exit(0)
except OSError, e:
print >>sys.stderr, "fork #2 failed: %d (%s)" % (e.errno, e.strerror)
sys.exit(1)
# start the daemon main loop
main()
This is one of the best books ever written. It covers these topics in great and extensive detail.
Advanced Programming in the UNIX Environment, Second Edition (Addison-Wesley Professional Computing Series) (Paperback)
ISBN-10: 0321525949
ISBN-13: 978-0321525949
5 star amazon reviews (I'd give it 6).
If the parent is a shell, and you want to launch a long running process then logout, consider nohup (1) or disown.
If you control the coding of the child, you can trap SIGHUP and handling it in some non-default way (like ignoring it outright). Read the signal (3) and sigaction (2) man pages for help with this. Either way there are several existing questions on StackOverflow with good help.