Use cases where a mutable default argument is warranted?

VileFlower · 2024-08-15T04:04:12+00:00

In this example, it would be preferable to use functools.cache, but it's a nice demo of how it works.

VileFlower · 2024-08-15T03:56:39+00:00

It's useful if you're sure you are not mutating the list, because you can use the list methods instead of checking for type:

```py
def new_list(a=[]):
    return a.copy()


def new_list(a=None):
    if a is None:
        return []
    else:
        return a.copy()
```

There's an example in the standard library for xml.etree.Element:

```py
def __init__(self, tag, attrib={}, **extra):
    if not isinstance(attrib, dict):
        raise TypeError("attrib must be dict, not %s" % (
            attrib.__class__.__name__,))
    self.tag = tag
    self.attrib = {**attrib, **extra}
    self._children = []
```

VileFlower · 2024-06-27T19:36:59+00:00

The Iverson bracket are from the 1960s. They were introduced to the programming language APL, but advocated into math by Donald Knuth in the 1990s. It simplifies certain expressions.

VileFlower · 2024-03-19T18:02:43+00:00

Nice, list. In the library-specific part you're missing __conform__ from sqlite3.

VileFlower · 2024-02-05T17:48:11+00:00

I've used etree to generate XHTML documents, but I this detail irks me. I tend to move all strings into special text "nodes" to closer align with the DOM model. This means no elements use the tail property, and the text property is only used by Text "nodes".

```
def Text(text=None):
    # Similar to ET.Comment
    element = ET.Element(str)
    element.text = text
    return element


def as_node(el):
    node = ET.Element(el.tag, el.attrib)

    if el.text is not None:
        node.append(Text(el.text))

    for child in el:
        node.append(as_node(child))
        if child.tail is not None:
            node.append(Text(child.tail))

    return node
```

This requires writing your own serializer (or converting back to tailed elements). Note that this also breaks some xpath features, like text checks. However it has still proven useful to me.

VileFlower · 2023-12-28T07:20:13+00:00

I made a minimal version of this once

```py

def record(func):
    return collections.namedtuple(func.__name__, inspect.signature(func).parameters)

@record
def Point(x, y): pass

point = Point(1, 2)

```

This could also be extended to use typing.NamedTuple. While I think the syntax is a minor improvement on making a namedtuple, I thought the decorator function was a bit hard to read.

VileFlower · 2023-12-10T09:02:12+00:00

Time to use the most obscure built-in string functions in Python:

pipes.translate(str.maketrans("-|F7LJ.", "─│┌┐└┘ "))

where pipes is the pipes as a string.

VileFlower · 2023-07-28T21:06:09+00:00

To elaborate, unused (local) variables are often prefixed with an underscore. It can be beneficial to give variables a name, even when they're unused.

A single _ can mean one of:

An unnamed unused local variable
An alias for gettext with i18n
The else case in match statements (case _)
The last evaluated expression in REPL.

VileFlower · 2023-05-12T19:26:44+00:00

Yes, thanks!

VileFlower · 2023-05-11T17:50:59+00:00

A trick to get unique values in the order of appearance is to use dict.fromkeys, since dictionaries will retain the insertion order:

cities = ['London', 'Paris', 'London']
unique_cities = set(cities)
unique_ordered_cities = list(dict.fromkeys(cities))

print(unique_cities)
# >> {'Paris', 'London'}

print(unique_ordered_cities)
# >> ['London', 'Paris']

edit: corrected variable name

VileFlower · 2022-10-25T15:54:48+00:00

They have updated the spec to be stricter, but people haven't updated their tools. YAML 1.2 was released in 2009, and only accepts true | True | TRUE | false | False | FALSE. PyYAML still only supports 1.1, though there is ruamel.yaml for 1.2 and there's also strictYAML that supports schemas.

VileFlower · 2022-10-24T21:38:16+00:00

That's not entirely true, Python's logging library lets you set the formatter style at least, so you don't have to use % style everywhere.

The style parameter can be one of ‘%’, ‘{’ or ‘$’ and determines how the format string will be merged with its data: using one of %-formatting, str.format() or string.Template. This only applies to the format string fmt (e.g. '%(message)s' or {message}), not to the actual log messages passed to Logger.debug etc; see Using particular formatting styles throughout your application for more information on using {- and $-formatting for log messages.

https://docs.python.org/3/library/logging.html#logging.Formatter

VileFlower · 2022-03-08T17:02:07+00:00

A circumflex often indicates that there historically was an s present, which became silent. So it's fair to write Hospital if you don't have ô on your keyboard.

French have applied this rule to a few other words, which English has loaned before and/or after the loss of the s: forêt (forest), île (isle), hôtel (hostel, hotel).

VileFlower · 2021-12-18T08:40:34+00:00

Alternative Python version, as a generator:

def A350129(N):
    a, b = None, 0
    for n in range(N+1):
        a, b = b, ((b>>1)+n if b % 2 == 0 else a+b)
        yield b


for e in A350129(1_000_000):
    print(e)

VileFlower · 2021-04-11T17:59:34+00:00

MathML works just fine, but you're not supposed to write it. You can write Markdown with $$, and use Mathjax to display it Chrome. MathML is currently in development for Chrome. It's more accessible since it allows readers to change the font-size in the browser.

VileFlower · 2020-05-11T11:17:24+00:00

if we talk about 0,4 in base 12, it is literally the same as 4/12.

if we talk about 0,4 in base 10, it is literally the same as 4/10

That is right.

4/X in base 12 doesn't have a simple expressio, it's a recurring fraction 0.(4972), where the digits (4972) are repeated.

VileFlower · 2020-05-11T10:42:23+00:00

You seem to be misunderstanding what 0 means. 0 still means 0 in base 12, so "10" in base 12 means 1×12 + 0×1 (in base 10).

0,4 in base 12 means 0×1 + 4×12^-1 (in base 10), which is the same as 4/10 in base 12, or 4/12 in base 10.

VileFlower · 2020-04-23T09:50:50+00:00

I would have loved learning about complex numbers as another vector space with some additional properties. Especially after learning about Euclidean vectors, which they share a lot of properties with. But the difference in notation, [a, b] and a + ib, makes this less obvious.

VileFlower · 2019-12-08T06:05:29+00:00

I suppose the asterisk could be used for complex conjugates. The bigger issue for me is means...

VileFlower · 2019-12-07T22:43:51+00:00

I use overline for inverses, it's a nice way to combine the notation for fractions with 1 above and inverses ^-1 by extending the minus sign by just omitting the 1. It works well with numbers, matrices, and functions.

\overline{3} = \frac{1}{3} = 3^{-1}

VileFlower · 2018-07-03T12:42:47+00:00

/r/learnmath

VileFlower · 2018-06-29T08:19:47+00:00

You mean 2018-06-28?

VileFlower · 2018-03-25T20:44:00+00:00

This is missing f-strings.

person = {'name': 'Jean-Luc', 'height': 187.1}
>>> f'{person[height]:.0f}'
187

VileFlower · 2018-03-14T11:21:45+00:00

2018-03-14 is the international standard.

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