I have an application, written in Python, which is used by a fairly technical audience (scientists).
I"m looking for a good way to make the application extensible by the users, i.e. a scripting/plugin architecture.
I am looking for something extremely lightweight. Most scripts, or plugins, are not going to be developed and distributed by a third-party and installed, but are going to be something whipped up by a user in a few minutes to automate a repeating task, add support for a file format, etc. So plugins should have the absolute minimum boilerplate code, and require no "installation" other than copying to a folder (so something like setuptools entry points, or the Zope plugin architecture seems like too much.)
Are there any systems like this already out there, or any projects that implement a similar scheme that I should look at for ideas / inspiration?
Building a minimal plugin architecture in Python absolute: Questions
How to get an absolute file path in Python
3 answers
Given a path such as "mydir/myfile.txt", how do I find the file"s absolute path relative to the current working directory in Python? E.g. on Windows, I might end up with:
"C:/example/cwd/mydir/myfile.txt"
Answer #1
>>> import os
>>> os.path.abspath("mydir/myfile.txt")
"C:/example/cwd/mydir/myfile.txt"
Also works if it is already an absolute path:
>>> import os
>>> os.path.abspath("C:/example/cwd/mydir/myfile.txt")
"C:/example/cwd/mydir/myfile.txt"
How to check if a path is absolute path or relative path in a cross-platform way with Python?
3 answers
UNIX absolute path starts with "/", whereas Windows starts with alphabet "C:" or "". Does python have a standard function to check if a path is absolute or relative?
Answer #1
os.path.isabs returns True if the path is absolute, False if not. The documentation says it works in windows (I can confirm it works in Linux personally).
os.path.isabs(my_path)
How to join absolute and relative urls?
3 answers
I have two urls:
url1 = "http://127.0.0.1/test1/test2/test3/test5.xml"
url2 = "../../test4/test6.xml"
How can I get an absolute url for url2?
Answer #1
You should use urlparse.urljoin :
>>> import urlparse
>>> urlparse.urljoin(url1, url2)
"http://127.0.0.1/test1/test4/test6.xml"
With Python 3 (where urlparse is renamed to urllib.parse) you could use it as follow:
>>> import urllib.parse
>>> urllib.parse.urljoin(url1, url2)
"http://127.0.0.1/test1/test4/test6.xml"
Building a minimal plugin architecture in Python 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)
0.37095273281943264
>>> timeit.timeit("[0] * 10", "import itertools", number = 1000000)
0.5577236771712819
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)
1.7508119747063233
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
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
time.sleep(60)
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,))
s.run()
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))
