How to repeat last command in python interpreter shell?

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How do I repeat the last command? The usual keys: Up, Ctrl+Up, Alt-p don"t work. They produce nonsensical characters.

(ve)[[email protected] ve]$ python
Python 2.6.6 (r266:84292, Nov 15 2010, 21:48:32) 
[GCC 4.4.4 20100630 (Red Hat 4.4.4-10)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> print "hello world"
hello world
>>> ^[[A
  File "<stdin>", line 1
SyntaxError: invalid syntax
>>> ^[[1;5A
  File "<stdin>", line 1
SyntaxError: invalid syntax
>>> ^[p
  File "<stdin>", line 1
SyntaxError: invalid syntax

How to repeat last command in python interpreter shell? repeat: Questions

Create list of single item repeated N times

5 answers

I want to create a series of lists, all of varying lengths. Each list will contain the same element e, repeated n times (where n = length of the list).

How do I create the lists, without using a list comprehension [e for number in xrange(n)] for each list?


Answer #1

You can also write:

[e] * n

You should note that if e is for example an empty list you get a list with n references to the same list, not n independent empty lists.

Performance testing

At first glance it seems that repeat is the fastest way to create a list with n identical elements:

>>> timeit.timeit("itertools.repeat(0, 10)", "import itertools", number = 1000000)
>>> timeit.timeit("[0] * 10", "import itertools", number = 1000000)

But wait - it"s not a fair test...

>>> itertools.repeat(0, 10)
repeat(0, 10)  # Not a list!!!

The function itertools.repeat doesn"t actually create the list, it just creates an object that can be used to create a list if you wish! Let"s try that again, but converting to a list:

>>> timeit.timeit("list(itertools.repeat(0, 10))", "import itertools", number = 1000000)

So if you want a list, use [e] * n. If you want to generate the elements lazily, use repeat.

What is the best way to repeatedly execute a function every x seconds?

5 answers

DavidM By DavidM

I want to repeatedly execute a function in Python every 60 seconds forever (just like an NSTimer in Objective C). This code will run as a daemon and is effectively like calling the python script every minute using a cron, but without requiring that to be set up by the user.

In this question about a cron implemented in Python, the solution appears to effectively just sleep() for x seconds. I don"t need such advanced functionality so perhaps something like this would work

while True:
    # Code executed here

Are there any foreseeable problems with this code?


Answer #1

If your program doesn"t have a event loop already, use the sched module, which implements a general purpose event scheduler.

import sched, time
s = sched.scheduler(time.time, time.sleep)
def do_something(sc): 
    print("Doing stuff...")
    # do your stuff
    s.enter(60, 1, do_something, (sc,))

s.enter(60, 1, do_something, (s,))

If you"re already using an event loop library like asyncio, trio, tkinter, PyQt5, gobject, kivy, and many others - just schedule the task using your existing event loop library"s methods, instead.


Answer #2

Lock your time loop to the system clock like this:

import time
starttime = time.time()
while True:
    print "tick"
    time.sleep(60.0 - ((time.time() - starttime) % 60.0))

How to repeat last command in python interpreter shell? StackOverflow: Questions


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