Vim & Vision

[ #241 ] Checking for exceptions in doctests Permalink

Python Added a day ago

You use the '...' magic:

http://stackoverflow.com/questions/12592/can-you-check-that-an-exception-is-thrown-with-doctest-in-python

Cached here:

>>> x
Traceback (most recent call last):
  ...
NameError: name 'x' is not defined

[ #240 ] Homer's Curling Speech Permalink

Comedy Added a day ago

Let us curl, milady. Let us throw and sweep atwain until the heavens themselves drop their jaws in wonder and envy. And afterwards there'll be beer and cocoa with marshmallows floating in the foam. And if, from now till the end of time, someone should ask what we were doing on the eve of the seventeenth of November, we shall proclaim that we were curling!

[ #238 ] retry in Python Permalink

Python Added a few days ago

If you want to wrap some code in a try/except block in Python, but you want it to be tried number of times before finally raising an exception, you can do something like this:

maxtries = 5
trynumber = 1
while 1:
    try:
        # your code here
    except WhateverException:
        if trynumber >= maxtries:
            # report your error
            raise SomeException
        # maybe sleep here
        trynumber += 1

This can be used for transient errors like network stuff...

This implements Ruby's begin/rescue/retry block (more messily of course.)

[ #237 ] Vim Makefile tabs Permalink

Makefile, Vim Added about three weeks ago

If, like me, you have your vim setup to do 4-space tabs, you will have a problem when you are editing Makefiles. Makefiles need real \t tabs. There are two ways to deal with this.

The first is manual: instead of pressing the tab key, press ctrl-v ctrl-i

The second way is using a vim comment hint like so:

# vim: noexpandtabs

... somewhere in your file. With this second method you can now simply press the tab key to get real tabs.

[ #236 ] Centos (or RH) IPTables Permalink

Linux Added about three weeks ago

When you try to test your new HTTP server installation on a Centos box, you will find that you get no response. That's because port 80 is firewalled by default. Add this new rule to your tables:

# iptables -I RH-Firewall-1-INPUT 6 -p tcp -m tcp --dport 80 -j ACCEPT
            ^                     ^                       ^       ^
            |            at position 6             the HTTP port  |    
    insert into RH-Firewall-1-INPUT chain                       allow :-)

Then after you've tested this change, make it permanent (otherwise it won't survive a reboot):

# service iptables save

You can check the rulesets at any time with:

# service iptables status

... and remember to do something similar if you have port 443 open for HTTPS...

[ #235 ] Converting ssh2 public keys to openssh Permalink

SSH, Shell Added about three weeks ago

Sometimes you will have to convert a public key generated by PuttyGen for use on *nix. Just use ssh-keygen:

ssh-keygen -i -f sshv2.pub > id_dsa.pub

[ #234 ] Vim comment hints Permalink

Vim, Python Added about three weeks ago

If you need vim to interpret a file in a specific way (or set some values for a specific file only), you can put comment hints in the file.

For example, if you have a Python file that doesn't have a .py extension and also doesn't have a #! line indicating that it is indeed Python, then vim will not turn on the correct syntax highlighting for your file (because it thinks it is just plain text.) To force Python syntax highlighting, place a comment hint at the bottom of your file like this:

def eggs():
    pass
# vim: syntax=python

[ #233 ] Context managers in Perl Permalink

Perl Added about a month ago

Let's try to implement something like Python's with statement in Perl.

First, let's look at Python. Python lets you do something like this:

class controlled_execution:
    def __enter__(self):
        set things up
        return thing
    def __exit__(self, type, value, traceback):
        tear things down

with controlled_execution() as thing:
     some code

(code example stolen from effbot)

The idea is that when the with block exits, the __exit__ cleanup is automatically called. This is nice for dealing with files, for example:

 with f = open("somefile"):
    f.read()

... where the implicit __exit__ code closes the file for us.

Can we do this in Perl? Sure. We just don't have the luxury of using nicely named __enter__ and __exit__ functions. Here is an example:

package Dir;

use strict;
use warnings;

use Cwd;

sub cd {
    my $dir = shift;
    my $code = shift;
    my $origdir = getcwd();
    chdir($dir);
    $code->();
    chdir($origdir);
}

1;

Now the script that utilises it:

#!/usr/bin/env perl

use strict;
use warnings;

use Dir;

Dir::cd "..", sub {
    my @files = glob("*");
    print join("\n", @files);
};

This context manager is for "cd", which chages directory, runs all the code in the block, and as it exits it simply changes back to the original directory it was in. There you go! Simple context managers in Perl.

[ #232 ] Dish rotation Permalink

Python Added about a month ago

James over at Prog21 has an article on calculating the shortest rotation (in degrees) for a satellite dish - his point being that there is a case or two that he didn't immediately think about (i.e. that it's harder than it sounds.)

Here is my Python version of his function (with doc tests):

def angle_diff(begin, end):
    """
    >>> angle_diff(0, 50)
    50
    >>> angle_diff(37, 38)
    1
    >>> angle_diff(200, 10)
    170
    >>> angle_diff(50, 20)
    -30
    >>> angle_diff(0, 270)
    -90
    >>> angle_diff(270, 0)
    90
    >>> angle_diff(100, 100)
    0
    >>> angle_diff(0, 0)
    0
    """
    easyway = end - begin
    if abs(easyway) > 180:
        return (360 - abs(easyway)) * cmp(0, easyway)
        # get the shorter way ^
        #           in the opposite direction ^
    return easyway

Testing:

$ nosetests --with-doctest ad.py 
.
----------------------------------------------------------------------
Ran 1 test in 0.003s

OK

[ #231 ] Git - fixing commit user Permalink

Git Added about a month ago

If you just committed a change as the incorrect user, as long as you haven't pushed your branch you can do this:

$ git config user.name "Correct name here"
$ git config user.email "Correct email here"
$ git commit --amend --reset-user

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