Skip to main content

how well do you know python, part 2

An easy one today: 
import os, threading

def foo(s):
    print s

for dir in os.listdir(os.getcwd()):
    threading.Thread(target=lambda: foo(dir)).start()
What bug may cause this to print something other than the contents of the current directory?

Comments

Ian Bicking said…
I feel like it's too soon to just answer straight out before other people try... how about...

print "Yrg'f fnl bf.yvfgqve(pjq)==['n', 'o']. Ba gur svefg eha guebhtu gur sbe ybbc, qve=='n', naq gur guernq vf fgnegrq. Vs nsgre gur guernq vf fgnegrq, ohg orsber vg trgf gb vaibxr sbb(qve) gur qve inevnoyr vf frg gb 'o' (orpnhfr gur ybbc vf eha gur frpbaq gvzr) gura sbb('o') jvyy or pnyyrq naq lbh'yy frr 'o\\ao\\a'".decode('rot13')
4:38 PM
Anonymous said…

for dir in os.listdir(os.getcwd()):
threading.Thread(target=foo, args=(dir,)).start()


Is the right way to do it ? Then dir would be evaluated at the Thread creation.
5:20 AM
Jonathan Ellis said…
That's probably the best way, yes.
6:41 AM
Anonymous said…
There's another common idiom which is doing something like:

lambda dir=dir: foo(dir)

OTOH, in this case there's already a standard way of passing arguments, as shown above.
7:35 AM
Anonymous said…
lamdba is evil.

using threading for output is a friend of lambda.

Harald Armin Massa notonblogger
3:47 AM
Anonymous said…
lambda is GOD!

How else would we say:

total_size = reduce( os.listdir(os.getcwd()), lambda a,x: a+os.stat(x).st_size,0 )

short, clear, and to the point
8:27 AM
Post a Comment

Popular posts from this blog

PyCon Python IDE review

I presented an IDE review at PyCon last Friday. It was basically a re-review of what I thought were the 3 most promising IDEs from the Utah Python User Group IDE review , to which I added SPE, which was by far the most popular of the ones we left out that time. The versions reviewed are: PyDev 1.0.2 SPE 0.8.2.a Komodo 3.5.2 Wing IDE 2.1 beta 1 I'd intended to base my presentation around a comparison of writing a smallish program in each of the IDEs, but the more I tried to make this not suck, the more I realized it was a losing proposition. Instead, I decided to try to focus on the features in each that most set them apart from the others (both positive and negative); this seemed more likely be useful. (I did a new feature matrix for this review, which is included after my comments. The slides I used are also up, at http://utahpython.org/jellis/pycon-ides.pdf , but aren't very useful absent video of the presentation itself. Hence this post.) PyDev PyDev has g...
43 comments
Read more

Troubleshooting the ps3 wireless network connection, including error 80130128

My father got a ps3 for Christmas, but ran into some problems getting it on his wireless network. The first one was "connection error 80130128" after configuring it to use DHCP. I couldn't google anything useful about this; just a few other hapless victims asking if anyone had any ideas. Fortunately Dad had his laptop there too and noticed Windows complaining that two machines on the network were both using the same IP. So, over the phone, I walked him through setting up the ps3 with a static address: on his laptop, run -> cmd ipconfig Read the "gateway" ip. Put that into his browser to go to his router's admin page Find the DHCP settings for his router to see what range of IPs it hands out; pick one outside that range Set up the ps3 with that IP, the router IP as primary dns, and an opendns server as secondary This made the connection test happy. But when he tried to go to the playstation store, it gave a DNS error. If he repeated the connection te...
7 comments
Read more

A review of 6 Python IDEs

(March 2006: you may also be interested the updated review I did for PyCon -- http://spyced.blogspot.com/2006/02/pycon-python-ide-review.html .) For September's meeting, the Utah Python User Group hosted an IDE shootout. 5 presenters reviewed 6 IDEs: PyDev 0.9.8.1 Eric3 3.7.1 Boa Constructor 0.4.4 BlackAdder 1.1 Komodo 3.1 Wing IDE 2.0.3 (The windows version was tested for all but Eric3, which was tested on Linux. Eric3 is based on Qt, which basically means you can't run it on Windows unless you've shelled out $$$ for a commerical Qt license, since there is no GPL version of Qt for Windows. Yes, there's Qt Free , but that's not exactly production-ready software.) Perhaps the most notable IDEs not included are SPE and DrPython. Alas, nobody had time to review these, but if you're looking for a free IDE perhaps you should include these in your search, because PyDev was the only one of the 3 free ones that we'd consider using. And if you aren...
36 comments
Read more