Style Transformation Javascript Scale

| | | |

Creating animated web elements is an important feature of web design. For example, you can design a button that you want to tilt when the user hovers over the button.

This is where the CSS transform property comes in. The transform property is used to move, rotate, tilt, and resize elements on a web page. This allows you to make a web page more interactive for the user.

This tutorial will explain, with examples, how to work with 2D transformations in CSS using the transform property. By the end of reading this tutorial, you will be an expert in using CSS 2D transformations.

CSS 2D Transformations

The CSS transform function allows you to create basic transformations of animations such as rotations, movements, scales and tilts on a Web page.

When an element is transformed, it has no effect on neighboring elements. However, a transformed element can overlap, although it will always take up space in its default location on a web page.

There are two types of transformations in CSS: 2D and 3D. The transform property is used to create transformations of both types, but for this article we will focus on 2D transformations.

There are a number of 2D transformations that can be applied to web elements in CSS. They are:

  • translate ()
  • scale ()
  • scaleX ()
  • scaleY () < / li>
  • skew ()
  • skewX ()
  • skewY ()
  • matrix ()
  • rotation () < / li>

We will analyze each of these transformations individually, referring to an example.

translate () Transformation

The translate () method allows you to move a item from its current position to a new position on the screen.

The translate () function accepts two parameters: the number of pixels to the right of the element must move and the number of pixels at the bottom of the element must move.

The syntax of this method is:

translate (xAxis, yAxis);

Suppose we have a box that we want to move 25px to the right and 50px down from its current position. We could do this using the following code:

This is a box that has been moved using the translate () method.

styles.css div {transform: translate (25px, 50px); background color: light blue; border: 3 pixels solid black ; }

Our code returns:

[Code result here]

On breaks down our code. In our HTML code, we have created two paragraphs of text. The first paragraph appears at the top of the page. The second paragraph appears below the first paragraph and is surrounded by a tag . This style sets the color of our box a solid black border that is 3 pixels wide. Additionally, we also used the translate () transformation to shift our box 25 pixels to the left and 50 pixels down.

Here is our code with no translate () transformation specified:

This is a box that has been moved using the translate () method.

styles.css div {background-color: lightblue; border: 3 pixels solid black ; }

Our code returns:

[Result code here]

How you can see, without specifying a translate () method, our box keeps its normal position on the web page.

rotate () transformation

The rotate () transformation allows you to rotate an element clockwise or counterclockwise. The extent of an element’s rotation is based on a given value in degrees.

The syntax of the rotate () transformation is as follows:

transform: rotation (Xdeg);

In the above syntax, X refers to the number of degrees an element has rotated. If you want to rotate an element clockwise, you must specify a positive value for X; otherwise, if you want to rotate an element counterclockwise, you need to specify a negative value for X.

Suppose we have a box that we want to rotate 45 degrees. We could rotate our box using the following code:

This is a box that has been rotated.

styles.css div {transform: rotation (45 degrees); background color: light blue; border: 3 pixels solid black ; }

Our code returns:

[Code result here]

On breaks down our code. In our HTML code, we have created a box 45 degrees clockwise.

As you can see from the output of our code, the box we created has been rotated. Here is a comparison of our pre-rotated and post-rotated boxes:

Screen Shot 2020 04 02 At 08.40.36

scale () transformation

The scale () method allows you to increase or decrease the size of an item.

The syntax of the scale () method is as follows:

transform: scale (x, y);

The scale function will proportionally resize the width (x) and height (y) of an image according to the specified values. If you don’t specify a value for the height scale, the scale () function will assume that the height scale should equal the width scale.

Suppose we have a box that we want to resize to 1.5 times its original size. We could do it using this code:

C ’is a box that has been resized.

styles.css div {transform: scale (1.5, 1.5); background color: light blue; border: 3 pixels solid black ; }

Our code returns:

[Result code here]

In the our HTML code, we created a box that contains a text sentence. In our CSS code, we specified that all

Screenshot 2020 04 02 at 08.37.38 ==" width = "260" src = "https://744025.smushcdn.com/1245953/wp-content/uploads/2020/04/Screen-Shot-2020-04- 02-at -08.37.38.jpg? Loss = 1 & undress = 1 & webp = 1 " alt =" Screenshot 2020 04 02 to 08.37.38 "class =" wp-image-14817 "srcset =" https: //744025.smushcdn.com/1245953/wp-content/uploads/ 2020/04 / Screen-Shot -2020-04-02-at-08.37.38.jpg? Lossy = 1 & strip = 1 & webp = 1 20w, https://744025.smushcdn.com/1245953/wp-content / uploads / 2020/04 / Screen-Shot-2020-04-02-at-08.37.38.jpg? Lossy = 1 & strip = 1 & webp = 1249w "size =" (max width: 249px) 100vw, 249px ">

Here is an image comparing the sizes of two boxes. The smallest box has no scale value () and the largest box has a scale () of 1.5:

The largest box, which includes the text This is a box that has been resized. is 1.5 times the size of our original box.

scaleX () transformation

The scaleX () transformation allows you to increase or decrease the width of an element. The syntax of the scaleX () transformation is:

transform: scaleX (xValue);

The xValue parameter is the amount by which you want to resize the width of an element. Suppose you have a box whose width you want to increase by a factor of 1.6. You can increase the size of this box by using the following code:

;

This is a box that has been resized.

styles.css div {transform: scaleX (1.5); background color: light blue; border: 3 pixels solid black ; }

Our code returns:

[Result code here]

In this for example, the width of our box has been increased by 1.5 times its original width.

the scaleY () transformation

The scaleY () allows you to increase or decrease the height of an element. scaleY () works the same as scaleX (), but instead of affecting the width of an element, scaleY () changes the height of the element.

Suppose we want to reduce the height of a box to half of its current height. We could do it using this code:

C ’is a box that has been resized.

styles.css div {transform: scaleY (0.5); background color: light blue; border: 3 pixels solid black ; }

Our code returns:

[Result code here]

In the our code, we reduced the height of our box (which is represented by the y-axis) by a factor of 0.5. In other words, our box is half its original height.

skew () transformation

The skew () transformation deforms an element along its x and y axes from the specified angles.

The syntax of the skew () method is as follows:

transform: skew (xValue, yValue);

xValue refers to how much an element should be tilted on its x axis and yValue refers to how much an element should be tilted on its y axis. Both values ‚Äã‚Äãshould be represented in degrees.

If no value is specified for yValue, no y axis misalignment will be applied.

Suppose we want to tilt a box 10 degrees on the x axis and 15 degrees on the y axis. We could do it using this code:

C ’is a box that has been warped.

styles.css div {transform: skew (10deg, 15deg); background color: light blue; border: 3 pixels solid black ; }

Our code returns:

In this example, we’ve tilted our box 10 degrees on the x axis and 15 degrees on the y axis.

skewX () and skewY () transformations

Like the scale () method, skew () a two secondary methods that are used to tilt an element along the x or y axis of an element.

To skew an element only along its X axis, you can use the skewX () method. The syntax of this method is as follows:

transform: skewX (xValue);

xValue is the number of degrees on the x-axis that an element should be tilted.

To skew an element along its Y axis, you can use the skewY () method. The syntax of the skewY () method is:

transform: skewY (yValue);

So if you want to tilt an element 10 degrees up or the Y axis, you can use this code:

Matrix transformation ()

The matrix () transformation performs all CSS 2D transformations on an element. Thus, matrix () can be used to apply translate, rotate, scale, and tilt transformations.

The matrix () function accepts six parameters that allow you to apply transformations to an element. The syntax of this method is as follows:

transform: matrix (scaleX (), skewY (), skewX (), scaleY (), translateX (), translateY ());

Suppose we want to create a box that uses the following transformations:

We could specify each of these transformations individually. However, in doing so, we would have to write many separate transformations. Instead, we can use the matrix () method to write these transformations using one line of code.

Here is the code we could use to create our box with the above transformations :

This is a box that has been distorted .

styles.css div {transform: matrix (1, 10, 10, 1.25, 25, 25); background color: light blue; border: 3 pixels solid black ; }

Our code returns:

[Result code here]

In the our code, we applied a tilt, scale, and translate transform to our box. We achieved this by using the matrix () method and passing the values ‚Äã‚Äãspecified above.

Conclusion

The transform property is used to apply transformations to an element in CSS. CSS offers a number of 2D transformations, including tilt, scale, rotate, and translate, which are used to transform web elements.

This tutorial explored the basics of CSS 2D transformations. You are now ready to start creating your 2D transformations like a professional web developer.

Style Transformation Javascript Scale exp: Questions

exp

How do I merge two dictionaries in a single expression (taking union of dictionaries)?

5 answers

Carl Meyer By Carl Meyer

I have two Python dictionaries, and I want to write a single expression that returns these two dictionaries, merged (i.e. taking the union). The update() method would be what I need, if it returned its result instead of modifying a dictionary in-place.

>>> x = {"a": 1, "b": 2}
>>> y = {"b": 10, "c": 11}
>>> z = x.update(y)
>>> print(z)
None
>>> x
{"a": 1, "b": 10, "c": 11}

How can I get that final merged dictionary in z, not x?

(To be extra-clear, the last-one-wins conflict-handling of dict.update() is what I"m looking for as well.)

5839

Answer #1

How can I merge two Python dictionaries in a single expression?

For dictionaries x and y, z becomes a shallowly-merged dictionary with values from y replacing those from x.

  • In Python 3.9.0 or greater (released 17 October 2020): PEP-584, discussed here, was implemented and provides the simplest method:

    z = x | y          # NOTE: 3.9+ ONLY
    
  • In Python 3.5 or greater:

    z = {**x, **y}
    
  • In Python 2, (or 3.4 or lower) write a function:

    def merge_two_dicts(x, y):
        z = x.copy()   # start with keys and values of x
        z.update(y)    # modifies z with keys and values of y
        return z
    

    and now:

    z = merge_two_dicts(x, y)
    

Explanation

Say you have two dictionaries and you want to merge them into a new dictionary without altering the original dictionaries:

x = {"a": 1, "b": 2}
y = {"b": 3, "c": 4}

The desired result is to get a new dictionary (z) with the values merged, and the second dictionary"s values overwriting those from the first.

>>> z
{"a": 1, "b": 3, "c": 4}

A new syntax for this, proposed in PEP 448 and available as of Python 3.5, is

z = {**x, **y}

And it is indeed a single expression.

Note that we can merge in with literal notation as well:

z = {**x, "foo": 1, "bar": 2, **y}

and now:

>>> z
{"a": 1, "b": 3, "foo": 1, "bar": 2, "c": 4}

It is now showing as implemented in the release schedule for 3.5, PEP 478, and it has now made its way into the What"s New in Python 3.5 document.

However, since many organizations are still on Python 2, you may wish to do this in a backward-compatible way. The classically Pythonic way, available in Python 2 and Python 3.0-3.4, is to do this as a two-step process:

z = x.copy()
z.update(y) # which returns None since it mutates z

In both approaches, y will come second and its values will replace x"s values, thus b will point to 3 in our final result.

Not yet on Python 3.5, but want a single expression

If you are not yet on Python 3.5 or need to write backward-compatible code, and you want this in a single expression, the most performant while the correct approach is to put it in a function:

def merge_two_dicts(x, y):
    """Given two dictionaries, merge them into a new dict as a shallow copy."""
    z = x.copy()
    z.update(y)
    return z

and then you have a single expression:

z = merge_two_dicts(x, y)

You can also make a function to merge an arbitrary number of dictionaries, from zero to a very large number:

def merge_dicts(*dict_args):
    """
    Given any number of dictionaries, shallow copy and merge into a new dict,
    precedence goes to key-value pairs in latter dictionaries.
    """
    result = {}
    for dictionary in dict_args:
        result.update(dictionary)
    return result

This function will work in Python 2 and 3 for all dictionaries. e.g. given dictionaries a to g:

z = merge_dicts(a, b, c, d, e, f, g) 

and key-value pairs in g will take precedence over dictionaries a to f, and so on.

Critiques of Other Answers

Don"t use what you see in the formerly accepted answer:

z = dict(x.items() + y.items())

In Python 2, you create two lists in memory for each dict, create a third list in memory with length equal to the length of the first two put together, and then discard all three lists to create the dict. In Python 3, this will fail because you"re adding two dict_items objects together, not two lists -

>>> c = dict(a.items() + b.items())
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unsupported operand type(s) for +: "dict_items" and "dict_items"

and you would have to explicitly create them as lists, e.g. z = dict(list(x.items()) + list(y.items())). This is a waste of resources and computation power.

Similarly, taking the union of items() in Python 3 (viewitems() in Python 2.7) will also fail when values are unhashable objects (like lists, for example). Even if your values are hashable, since sets are semantically unordered, the behavior is undefined in regards to precedence. So don"t do this:

>>> c = dict(a.items() | b.items())

This example demonstrates what happens when values are unhashable:

>>> x = {"a": []}
>>> y = {"b": []}
>>> dict(x.items() | y.items())
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: unhashable type: "list"

Here"s an example where y should have precedence, but instead the value from x is retained due to the arbitrary order of sets:

>>> x = {"a": 2}
>>> y = {"a": 1}
>>> dict(x.items() | y.items())
{"a": 2}

Another hack you should not use:

z = dict(x, **y)

This uses the dict constructor and is very fast and memory-efficient (even slightly more so than our two-step process) but unless you know precisely what is happening here (that is, the second dict is being passed as keyword arguments to the dict constructor), it"s difficult to read, it"s not the intended usage, and so it is not Pythonic.

Here"s an example of the usage being remediated in django.

Dictionaries are intended to take hashable keys (e.g. frozensets or tuples), but this method fails in Python 3 when keys are not strings.

>>> c = dict(a, **b)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: keyword arguments must be strings

From the mailing list, Guido van Rossum, the creator of the language, wrote:

I am fine with declaring dict({}, **{1:3}) illegal, since after all it is abuse of the ** mechanism.

and

Apparently dict(x, **y) is going around as "cool hack" for "call x.update(y) and return x". Personally, I find it more despicable than cool.

It is my understanding (as well as the understanding of the creator of the language) that the intended usage for dict(**y) is for creating dictionaries for readability purposes, e.g.:

dict(a=1, b=10, c=11)

instead of

{"a": 1, "b": 10, "c": 11}

Response to comments

Despite what Guido says, dict(x, **y) is in line with the dict specification, which btw. works for both Python 2 and 3. The fact that this only works for string keys is a direct consequence of how keyword parameters work and not a short-coming of dict. Nor is using the ** operator in this place an abuse of the mechanism, in fact, ** was designed precisely to pass dictionaries as keywords.

Again, it doesn"t work for 3 when keys are not strings. The implicit calling contract is that namespaces take ordinary dictionaries, while users must only pass keyword arguments that are strings. All other callables enforced it. dict broke this consistency in Python 2:

>>> foo(**{("a", "b"): None})
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: foo() keywords must be strings
>>> dict(**{("a", "b"): None})
{("a", "b"): None}

This inconsistency was bad given other implementations of Python (PyPy, Jython, IronPython). Thus it was fixed in Python 3, as this usage could be a breaking change.

I submit to you that it is malicious incompetence to intentionally write code that only works in one version of a language or that only works given certain arbitrary constraints.

More comments:

dict(x.items() + y.items()) is still the most readable solution for Python 2. Readability counts.

My response: merge_two_dicts(x, y) actually seems much clearer to me, if we"re actually concerned about readability. And it is not forward compatible, as Python 2 is increasingly deprecated.

{**x, **y} does not seem to handle nested dictionaries. the contents of nested keys are simply overwritten, not merged [...] I ended up being burnt by these answers that do not merge recursively and I was surprised no one mentioned it. In my interpretation of the word "merging" these answers describe "updating one dict with another", and not merging.

Yes. I must refer you back to the question, which is asking for a shallow merge of two dictionaries, with the first"s values being overwritten by the second"s - in a single expression.

Assuming two dictionaries of dictionaries, one might recursively merge them in a single function, but you should be careful not to modify the dictionaries from either source, and the surest way to avoid that is to make a copy when assigning values. As keys must be hashable and are usually therefore immutable, it is pointless to copy them:

from copy import deepcopy

def dict_of_dicts_merge(x, y):
    z = {}
    overlapping_keys = x.keys() & y.keys()
    for key in overlapping_keys:
        z[key] = dict_of_dicts_merge(x[key], y[key])
    for key in x.keys() - overlapping_keys:
        z[key] = deepcopy(x[key])
    for key in y.keys() - overlapping_keys:
        z[key] = deepcopy(y[key])
    return z

Usage:

>>> x = {"a":{1:{}}, "b": {2:{}}}
>>> y = {"b":{10:{}}, "c": {11:{}}}
>>> dict_of_dicts_merge(x, y)
{"b": {2: {}, 10: {}}, "a": {1: {}}, "c": {11: {}}}

Coming up with contingencies for other value types is far beyond the scope of this question, so I will point you at my answer to the canonical question on a "Dictionaries of dictionaries merge".

Less Performant But Correct Ad-hocs

These approaches are less performant, but they will provide correct behavior. They will be much less performant than copy and update or the new unpacking because they iterate through each key-value pair at a higher level of abstraction, but they do respect the order of precedence (latter dictionaries have precedence)

You can also chain the dictionaries manually inside a dict comprehension:

{k: v for d in dicts for k, v in d.items()} # iteritems in Python 2.7

or in Python 2.6 (and perhaps as early as 2.4 when generator expressions were introduced):

dict((k, v) for d in dicts for k, v in d.items()) # iteritems in Python 2

itertools.chain will chain the iterators over the key-value pairs in the correct order:

from itertools import chain
z = dict(chain(x.items(), y.items())) # iteritems in Python 2

Performance Analysis

I"m only going to do the performance analysis of the usages known to behave correctly. (Self-contained so you can copy and paste yourself.)

from timeit import repeat
from itertools import chain

x = dict.fromkeys("abcdefg")
y = dict.fromkeys("efghijk")

def merge_two_dicts(x, y):
    z = x.copy()
    z.update(y)
    return z

min(repeat(lambda: {**x, **y}))
min(repeat(lambda: merge_two_dicts(x, y)))
min(repeat(lambda: {k: v for d in (x, y) for k, v in d.items()}))
min(repeat(lambda: dict(chain(x.items(), y.items()))))
min(repeat(lambda: dict(item for d in (x, y) for item in d.items())))

In Python 3.8.1, NixOS:

>>> min(repeat(lambda: {**x, **y}))
1.0804965235292912
>>> min(repeat(lambda: merge_two_dicts(x, y)))
1.636518670246005
>>> min(repeat(lambda: {k: v for d in (x, y) for k, v in d.items()}))
3.1779992282390594
>>> min(repeat(lambda: dict(chain(x.items(), y.items()))))
2.740647904574871
>>> min(repeat(lambda: dict(item for d in (x, y) for item in d.items())))
4.266070580109954
$ uname -a
Linux nixos 4.19.113 #1-NixOS SMP Wed Mar 25 07:06:15 UTC 2020 x86_64 GNU/Linux

Resources on Dictionaries

5839

Answer #2

In your case, what you can do is:

z = dict(list(x.items()) + list(y.items()))

This will, as you want it, put the final dict in z, and make the value for key b be properly overridden by the second (y) dict"s value:

>>> x = {"a":1, "b": 2}
>>> y = {"b":10, "c": 11}
>>> z = dict(list(x.items()) + list(y.items()))
>>> z
{"a": 1, "c": 11, "b": 10}

If you use Python 2, you can even remove the list() calls. To create z:

>>> z = dict(x.items() + y.items())
>>> z
{"a": 1, "c": 11, "b": 10}

If you use Python version 3.9.0a4 or greater, then you can directly use:

x = {"a":1, "b": 2}
y = {"b":10, "c": 11}
z = x | y
print(z)
{"a": 1, "c": 11, "b": 10}

5839

Answer #3

An alternative:

z = x.copy()
z.update(y)

Style Transformation Javascript Scale JavaScript: Questions

JavaScript

JSON datetime between Python and JavaScript

4 answers

kevin By kevin

I want to send a datetime.datetime object in serialized form from Python using JSON and de-serialize in JavaScript using JSON. What is the best way to do this?

403

Answer #1

You can add the "default" parameter to json.dumps to handle this:

date_handler = lambda obj: (
    obj.isoformat()
    if isinstance(obj, (datetime.datetime, datetime.date))
    else None
)
json.dumps(datetime.datetime.now(), default=date_handler)
""2010-04-20T20:08:21.634121""

Which is ISO 8601 format.

A more comprehensive default handler function:

def handler(obj):
    if hasattr(obj, "isoformat"):
        return obj.isoformat()
    elif isinstance(obj, ...):
        return ...
    else:
        raise TypeError, "Object of type %s with value of %s is not JSON serializable" % (type(obj), repr(obj))

Update: Added output of type as well as value.
Update: Also handle date

JavaScript

What blocks Ruby, Python to get Javascript V8 speed?

4 answers

Are there any Ruby / Python features that are blocking implementation of optimizations (e.g. inline caching) V8 engine has?

Python is co-developed by Google guys so it shouldn"t be blocked by software patents.

Or this is rather matter of resources put into the V8 project by Google.

260

Answer #1

What blocks Ruby, Python to get Javascript V8 speed?

Nothing.

Well, okay: money. (And time, people, resources, but if you have money, you can buy those.)

V8 has a team of brilliant, highly-specialized, highly-experienced (and thus highly-paid) engineers working on it, that have decades of experience (I"m talking individually – collectively it"s more like centuries) in creating high-performance execution engines for dynamic OO languages. They are basically the same people who also created the Sun HotSpot JVM (among many others).

Lars Bak, the lead developer, has been literally working on VMs for 25 years (and all of those VMs have lead up to V8), which is basically his entire (professional) life. Some of the people writing Ruby VMs aren"t even 25 years old.

Are there any Ruby / Python features that are blocking implementation of optimizations (e.g. inline caching) V8 engine has?

Given that at least IronRuby, JRuby, MagLev, MacRuby and Rubinius have either monomorphic (IronRuby) or polymorphic inline caching, the answer is obviously no.

Modern Ruby implementations already do a great deal of optimizations. For example, for certain operations, Rubinius"s Hash class is faster than YARV"s. Now, this doesn"t sound terribly exciting until you realize that Rubinius"s Hash class is implemented in 100% pure Ruby, while YARV"s is implemented in 100% hand-optimized C.

So, at least in some cases, Rubinius can generate better code than GCC!

Or this is rather matter of resources put into the V8 project by Google.

Yes. Not just Google. The lineage of V8"s source code is 25 years old now. The people who are working on V8 also created the Self VM (to this day one of the fastest dynamic OO language execution engines ever created), the Animorphic Smalltalk VM (to this day one of the fastest Smalltalk execution engines ever created), the HotSpot JVM (the fastest JVM ever created, probably the fastest VM period) and OOVM (one of the most efficient Smalltalk VMs ever created).

In fact, Lars Bak, the lead developer of V8, worked on every single one of those, plus a few others.

JavaScript

Django Template Variables and Javascript

4 answers

When I render a page using the Django template renderer, I can pass in a dictionary variable containing various values to manipulate them in the page using {{ myVar }}.

Is there a way to access the same variable in Javascript (perhaps using the DOM, I don"t know how Django makes the variables accessible)? I want to be able to lookup details using an AJAX lookup based on the values contained in the variables passed in.

256

Answer #1

The {{variable}} is substituted directly into the HTML. Do a view source; it isn"t a "variable" or anything like it. It"s just rendered text.

Having said that, you can put this kind of substitution into your JavaScript.

<script type="text/javascript"> 
   var a = "{{someDjangoVariable}}";
</script>

This gives you "dynamic" javascript.

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