{"id":5816,"date":"2020-05-18T21:20:30","date_gmt":"2020-05-18T21:20:30","guid":{"rendered":"https:\/\/www.askpython.com\/?p=5816"},"modified":"2022-07-07T07:08:03","modified_gmt":"2022-07-07T07:08:03","slug":"python-wait-for-a-specific-time","status":"publish","type":"post","link":"https:\/\/www.askpython.com\/python\/examples\/python-wait-for-a-specific-time","title":{"rendered":"How to Wait for a Specific Time in Python?"},"content":{"rendered":"\n

Hello everyone! In this post, we’ll look at how we can wait for a specific time in Python.<\/p>\n\n\n\n

This is particularly important when you have certain events or tasks scheduled after a specific period of time.<\/p>\n\n\n\n

Python offers us different ways to do this. So let’s look at all the approaches that we can use: both in a single-threaded as well as a multi-threaded environment!<\/p>\n\n\n\n

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Python – Wait for a Specific Time in Single-Threaded Environments<\/h2>\n\n\n\n

If your main program consists only of a single thread \/ program, then Python makes this very easy for us.<\/p>\n\n\n\n

One possible approach to make a program wait for a specific time in Python is using the time <\/a><\/strong>module.<\/p>\n\n\n\n

Using time.sleep() to wait<\/h3>\n\n\n\n

We can use time.sleep(n)<\/code> to wait for n<\/code> seconds. Of course, we can make n<\/code> to be decimal to be more precise with our interval!<\/p>\n\n\n\n

Here is a simple example, which schedules two function calls between 3 seconds within each other.<\/p>\n\n\n

\nimport time\n\ndef fun1(a):\n    return 2 * a\n\ndef fun2(a):\n    return a * a\n\nif __name__ == '__main__':\n    inp = 10\n    print(f"Input = {inp}")\n    print(f"Result of fun1 call: {fun1(inp)}")\n    time.sleep(3) # Wait for 3 seconds\n    print(f"After 3 milliseconds, Result of fun2 call: {fun2(inp)}")\n<\/pre><\/div>\n\n\n
Output<\/strong><\/p>\n\n\n
\nInput = 10\nResult of fun1 call: 20\nAfter 3 seconds, Result of fun2 call: 100\n<\/pre><\/div>\n\n\n
Simple enough, right?<\/p>\n\n\n\n
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Waiting in a Multi-Threaded Environment<\/h2>\n\n\n\n
If you’re having multiple threads in your program, you can still use the same logic via time.sleep()<\/code> to make a particular thread wait for a specific time in Python<\/p>\n\n\n\n
Here is an example, which spawns 3 threads, and makes them sleep for a second alternatively, while the other threads keep printing numbers from 1.<\/p>\n\n\n\n
We’ll use the concurrent.futures<\/code> module and use the ThreadPoolExecutor<\/code> to pool and execute threads, while fetching the results using as_completed()<\/code>.<\/p>\n\n\n\n
The basic structure of spawning and fetching using threads is as follows:<\/p>\n\n\n
\nfrom concurrent.futures import ThreadPoolExecutor, as_completed\n\n# The threads will call this function\ndef callback():\n    pass\n\nwith ThreadPoolExecutor() as thread_executor:\n    # Await all results\n    await_results = [thread_executor.submit(callback) for i in range(1, tid+1)]\n    # Fetch them!\n    for f in as_completed([future for future in await_results]):\n        print(f.result())\n<\/pre><\/div>\n\n\n
Now, let’s write the code for our main program.<\/p>\n\n\n
\nfrom concurrent.futures import ThreadPoolExecutor, as_completed\nimport time\n\n# Global Variable for the Thread ID Number\ntid = 0\n# Spawn 4 threads\nNUM_THREADS = 4\n\ndef func(arg):\n    time.sleep(1)\n    return arg * arg\n\nif __name__ == '__main__':\n    with ThreadPoolExecutor() as thread_executor:\n        start_time = time.time()\n        # Going to spawn threads\n        tid += NUM_THREADS\n        # Await all results\n        await_results = [thread_executor.submit(func, arg=i) for i in range(1, tid+1)]\n        for f in as_completed([future for future in await_results]):\n            print(f.result())\n        end_time = time.time()\n        print(f"Total Time taken for {NUM_THREADS} threads: {end_time - start_time}")\n<\/pre><\/div>\n\n\n
Output<\/strong><\/p>\n\n\n
\n1\n4\n9\n16\nTotal Time taken for 4 threads: 1.0037879943847656\n<\/pre><\/div>\n\n\n
As you can see, we spawned 4 threads, who all waited for 1 second before giving the result of the function. This is very close to 1 second, so our output makes sense!<\/p>\n\n\n\n
Using threading.Timer() to schedule function calls<\/h3>\n\n\n\n
However, if you want a particular function to wait for a specific time in Python, we can use the threading.Timer()<\/code> method from the threading<\/code> module.<\/p>\n\n\n\n
We’ll show a simple example, which schedules a function call every 5 seconds.<\/p>\n\n\n
\nfrom threading import Timer\nimport time\n\ndef func(a, b):\n    print("Called function")\n    return a * b\n\n# Schedule a timer for 5 seconds\n# We pass arguments 3 and 4\nt = Timer(5.0, func, [3, 4])\n\nstart_time = time.time()\n\n# Start the timer\nt.start()\n\nend_time = time.time()\n\nif end_time - start_time < 5.0:\n    print("Timer will wait for sometime before calling the function")\nelse:\n    print("5 seconds already passed. Timer finished calling func()")\n<\/pre><\/div>\n\n\n
Output<\/strong><\/p>\n\n\n
\nTimer will wait for sometime before calling the function\nCalled function\n<\/pre><\/div>\n\n\n
Here, the main program came to the last line before 5 seconds were up, so Timer makes the program wait until it calls func()<\/code>.<\/p>\n\n\n\n
After calling func(a, b)<\/code>, it terminates the program, since there is nothing else to run.<\/p>\n\n\n\n
Also notice that the return value of the function cannot be used by the main program.<\/p>\n\n\n\n
Hopefully, this gave you some more ideas about scheduling and waiting for intervals.<\/p>\n\n\n\n
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Conclusion<\/h2>\n\n\n\n
In this article, we learned about waiting for a specific period of time in Python, using time.sleep()<\/code>. We also saw how we could use this in a Multi-Threaded environment, as well as scheduling function calls.<\/p>\n\n\n\n
References<\/h2>\n\n\n\n