DEV Community: Musale Martin

Select all nodes in a DOM except the nth query

Musale Martin — Tue, 07 Jul 2020 09:15:27 +0000

Say you have a HTML structure like this one:

<body>
    <div>
        <span style="font-weight:bold;">More Lorem Ipsum text: </span>
        <span>And More Lorem Ipsum text</span>
        <span>Some More Lorem Ipsum text</span>
        <span>Get Some More Lorem Ipsum text</span>
        <span>Finally Some More Lorem Ipsum text</span> In conclusion.
    </div>
</body>

I would like to apply some styling to the first span and then I change the remaining spans into text nodes.

The challenge I had was figuring out how to get the rest of the spans after the first. Turns out, it's quite simple:

const spans = document.querySelectorAll("span:not(:nth-child(1))")
spans.forEach(span => {
    const spanTxt = span?.textContent;
    if (spanTxt) span.replaceWith(spanTxt.trim())
})

That JavaScript (TypeScript) code will result to:

<body>
    <div>
        <span style="font-weight:bold;">More Lorem Ipsum text:</span> And More Lorem Ipsum text Some More Lorem Ipsum text Get Some More Lorem Ipsum text Finally Some More Lorem Ipsum text In conclusion.
    </div>
</body>

Fix and Recover a "corrupt history file" in ZSH

Musale Martin — Thu, 25 Jun 2020 11:41:25 +0000

Move to the home directory
$ cd ~

Move the .zsh_history file into another .zsh_history_bad file

$ mv .zsh_history .zsh_history_bad

Write all printable strings into a new .zsh_history file

$ strings .zsh_history_bad > .zsh_history

Finally, reload the history.

$ fc -R .zsh_history

Happy ZSH-ing!

(Un)Commenting Multiple Lines

Musale Martin — Wed, 24 Jun 2020 09:16:28 +0000

Commenting multiple lines

Move the cursor to the start line of the comment.
Press ESC to enter insert mode.
Press ctrl+v to enter visual block mode.
Use up and down arrows or shift+] to select the lines you want to comment on.
Press shift + I to enter insert mode.
Enter the comment character i.e. #.
Press ESC then ESC (ESC twice).

Uncommenting multiple lines

Move the cursor to the start line to uncomment.
Press ESC to enter insert mode.
Press ctrl+v to enter visual block mode.
Use up and down arrows or shift+] to select the lines you want to uncomment.
Press X or D to delete the comment character.

Happy hacking on VIM!

The Visitor Design Pattern

Musale Martin — Tue, 12 May 2020 17:33:19 +0000

Using an example of cocktails. Say we have a Cocktail that we can use to "make" different kinds of cocktails, like Mojito and Daiquiri. We can have a Cocktail interface that defines Serve and Drink methods for a cocktail:

type Cocktail interface{
    Serve()
    Drink()
}

You can make the Mojito and Daiquiri implement the Cocktail interface methods like this:

type Mojito struct{}

func(m Mojito) Serve(){}
func(m Mojito) Drink(){}

type Daiquiri struct{}

func(m Daiquiri) Serve(){}
func(m Daiquiri) Drink(){}

The challenge

Now, we want to be able to define new Cocktail operations without having to add the new methods on each existing cocktail. For the above implementation, we'll have to add the method in the Cocktail interface and then implement the method for each of the cocktails that we want to implement the method.

The visitor pattern will allow you to operate on a Cocktail so that you can provide a Cocktail that easily conforms to all the cocktail operations. It makes it easier to add new ways to work on a cocktail without getting to make the change on every cocktail.

The Visitor Pattern

To achieve this, we implement a new interface; CocktailVisitor that defines the visitor operations on a cocktail.

type CocktailVisitor interface{
    visitMojito(c Mojito)
    visitDaiquiri(c Daiquiri)
}

Next, we need to "route" the correct cocktail to the correct method on the visitor by changing the Cocktail interface.

type Cocktail interface{
    accept(v CocktailVisitor)
}

With that, we are now able to make the Cocktail interface to have a method accept that takes in a CocktailVisitor or any object "that is" a CocktailVisitor.

Finally, we make the cocktails:

type Mojito struct{}
func (m Mojito) accept(v CocktailVisitor){
    v.visitMojito(m)
}

type Daiquiri struct{}
func (d Daiquiri) accept(v CocktailVisitor){
    v.visitDaiquiri(d)
}

Now, if you need to add a new cocktail like a Margharita, you just have to implement its visitor and add it to the CocktailVisitor.

Usage

You will need to define the operation you want to accomplish. We want to do a DrinkVisit operation:

type DrinkVisit struct{}

func (DrinkVisit) visitMojito(m Mojito) {
    fmt.Println("Drinking mojitos")
}
func (DrinkVisit) visitDaiquiri(d Daiquiri) {
    fmt.Println("Drinking daiquiris")
}

Then we do the magic like:

func main() {
    visitor := DrinkVisit{}
    mojito := &Mojito{}
    daiquiri := &Daiquiri{}
    mojito.accept(visitor)
    daiquiri.accept(visitor)
}

A working play example can be found here

Conclusion

The visitor pattern is a common pattern in language interpreters that allows the interpreter to work on various expressions by defining operations on them. Typically, the accept method will return an interface{} or a value. That is well beyond the scope of this write-up.

Initially posted at musale.github.io

Python Sorting

Musale Martin — Mon, 26 Aug 2019 23:26:46 +0000

Introduction

Sorting is a common functionality in day-to-day programming. If you use Python, you are probably familiar with the two common ways you can sort your list values. The sorted() function is a common way to sort any iterable while list.sort() is built into the list. The main difference between the two functions is that list.sort() modifies the list in-place while sorted() creates a new list of sorted items.

Basic sorting

>>> sorted([4, 1, 3, 5, 2, 5, 8])
[1, 2, 3, 4, 5, 5, 8]
>>> l = [8, 24, 63, 12, 5, 23, 2, 6, 7, 8]
>>> l.sort()
>>> l
[2, 5, 6, 7, 8, 8, 12, 23, 24, 63]

Tip 1: Reverse ordering

Both methods allow an optional reverse key which is a boolean value. You can use this to change the order of the sort from ascending to descending.

>>> sorted([4, 1, 3, 5, 2, 5, 8], reverse=True)
[8, 5, 5, 4, 3, 2, 1]

Tip 2: Key function

The 2 list methods have a key function which allows you to pass in a function that is run before sorting each value.

For instance, if I want to order a string using the upper case I would do:

>>> sorted("For instance, if I want to order a".split(), key=str.upper)
['a', 'For', 'I', 'if', 'instance,', 'order', 'to', 'want']

For some cases, you might have a list of complex objects which you want to sort with their own index. You can pass a function referencing the index:

Say you have a list of handbag objects with Name, Size and Price properties, you can sort them with the Price like:

>>> handbags = [("Gucci", "L", 123), ("Vuitton", "M", 251), ("Jacobs", "S", 207)]
>>> handbags.sort(key=lambda bag: bag[2] )
>>> handbags
[('Gucci', 'L', 123), ('Jacobs', 'S', 207), ('Vuitton', 'M', 251)]

Tip 3: Multiple Level Sorting

Suppose you want to sort the bags according to their Price and Size, you can get that done by using Python's operator module which provides itemgetter and attrgetter.

>>> from operator import itemgetter, attrgetter
>>> sorted(handbags, key=itemgetter(1,2))
[('Gucci', 'L', 123), ('Vuitton', 'M', 251), ('Jacobs', 'S', 207)]

Or make it a list of objects with named attributes and use the names to sort:

>>> class Bag:
...    def __init__(self, name, size, price):
...      self.name = name
...      self.price = price
...      self.size = size
...    def __repr__(self):
...      return repr((self.name, self.size, self.price))
...
>>> bags = [Bag("Gucci", "L", 123), Bag("Vuitton", "M", 251), Bag("Jacobs", "S", 207)]
>>> bags.sort(key=attrgetter("price", "size"))
>>> bags
[('Gucci', 'L', 123), ('Jacobs', 'S', 207), ('Vuitton', 'M', 251)]

Conclusion

Sorting list items in Python is pretty easy and these tips can be used to achieve even much more with very little coding complexity. If you're worried about the stability of the sorting, Python sorts are guaranteed to be stable. That means that when multiple records have the same key, their original order is preserved.
Python uses Timsort algorithm that does multiple sorts efficiently because it can take advantage of any ordering already present in a dataset. You can read more about sorting in Python here

Adjusting Arch Linux time to local time

Musale Martin — Tue, 03 Apr 2018 11:21:10 +0000

After updating my system, I found out that the system time being displayed was 1 hour ahead. In fact, I thought I was late for lunch only to realize that the clock was one hour ahead.

Looking through the internet, I came across many solutions that didn't work. However, this proved to work. After checking the timedatectl status:

$ timedatectl status
$ Local time: Tue 2018-04-03 15:02:23
  Universal time: Tue 2018-04-03 12:02:23 UTC
  RTC time: Tue 2018-04-03 12:02:23
  Time zone: Africa/Nairobi (EAT, +0300)
  System clock synchronized: no
  systemd-timesyncd.service active: no
  RTC in local TZ: no

Combing around, the simple fix was to run:

$ timedatectl set-ntp true

Boom! On the next clock tick, the time adjusted correctly.

Motivation

You might face this issue if you update your Arch Linux to the latest release so in case you do, don't break a sweat 😉

fixing vagrant up ns_error_failure

Musale Martin — Tue, 30 May 2017 15:39:19 +0000

Today I installed Vagrant on a freshly installed OS and then when I ran a spun a test box, I came across this error

bug@bug ~/vm % vagrant up                                                                                                                                                                    (env: achieve) 
Bringing machine 'default' up with 'virtualbox' provider...
[default] Clearing any previously set forwarded ports...
[default] Clearing any previously set network interfaces...
There was an error while executing `VBoxManage`, a CLI used by Vagrant
for controlling VirtualBox. The command and stderr is shown below.

Command: ["hostonlyif", "create"]

Stderr: 0%...
Progress state: NS_ERROR_FAILURE
VBoxManage: error: Failed to create the host-only adapter
VBoxManage: error: VBoxNetAdpCtl: Error while adding new interface: failed to open /dev/vboxnetctl: No such file or directory
VBoxManage: error: Details: code NS_ERROR_FAILURE (0x80004005), component HostNetworkInterface, interface IHostNetworkInterface
VBoxManage: error: Context: "int handleCreate(HandlerArg*, int, int*)" at line 66 of file VBoxManageHostonly.cpp

I checked around the docs for Manjaro but I din't see this highlighted when you do an installation.

You have to reload virtualbox via CLI:

bug@bug ~/vm % sudo vboxreload

You are sorted!

Who am I?

Musale Martin — Tue, 23 May 2017 12:28:40 +0000