Programming homework and newbie help thread - Page 76 - Computer Technical Help

I'm using document.write but having weird problems with functions I've declared inside the HTML i'm writing.

particularly anything that gets called by "onclick" events that i declare in the tag. I probably should not do that in the tag and add an eventlistener but I'm not sure if that's what the real problem is.

Quote

05-08-2018 , 02:35 AM

#1877

jmakin

banned

Join Date: Jan 2008 Posts: 30,120

but thanks so much guys. I'm so bad at JS. it's so frustrating debugging php/JS.

one last thing if you wanna be super duper helpful, by tomorrow morning for 25% of the grade I have to come up with 2 "non trivial" uses of AJAX. What would be some easy to implement things that just use vanilla JS and look cool?

i have basic forms to submit and some product info but that's about the whole website. It's ecommerce related.

Quote

05-08-2018 , 05:46 AM

#1878

_dave_

_Pooh_Bah_

Join Date: Feb 2005 Posts: 13,146

Quote:

Originally Posted by jmakin

*disclaimer - it's been ages since I've used document.write so this may be wrong...

This is a situation where you'll be wanting to target an existing DIV tag to output your results. Calling a document.write from an onClick handler (so, after the document has finished loading) will emit the output after the closing </body></html> tags, so it probably won't be shown or it seems in Firefox it starts a new document (replacing what's already there entirely)

Try this:

Code:

<html>

<body>
  <script>
    document.write('<h1>A Simple Demo</h1>');
  </script>
  <a href="" onClick="document.getElementById('resultarea').innerHTML = '<h2>You clicked link A</h2>'; return false;">Link A</a>
  <br/>
  <a href="" onClick="document.getElementById('resultarea').innerHTML = '<h2>You clicked link B</h2>'; return false;">Link B</a>
  <br/>
  <a href="" onClick="document.write('<h2>You clicked link C</h2>'); return false;">Link C</a>
  <br/>
  <div id="resultarea"></div>
</body>

</html>

Hopefully demonstrates how things work.

Quote

05-08-2018 , 05:51 AM

#1879

_dave_

_Pooh_Bah_

Join Date: Feb 2005 Posts: 13,146

Ideas for non-trivial AJAX ecommerce related...

An auto-suggesting search? that would be 2 ajaxes, one for the autocomplete and one for the results. Probably way too "non-trivial"...

Quote

05-08-2018 , 10:22 AM

#1880

jmakin

banned

Join Date: Jan 2008 Posts: 30,120

Yea that makes sense.

They suggested auto complete But I already have auto complete implemented in my HTML and didn’t really want to rewrite it. I have a few hours and I can afford to tank this assignment, but I was thinking of sending an email of the form information to the user. Not sure how complicated this would be, it seems like PHP has good support for it

Quote

05-08-2018 , 03:23 PM

#1881

RustyBrooks

Carpal \'Tunnel

Join Date: Feb 2006 Posts: 24,647

Programmer tendencies in a nutshell:
https://github.com/urigoren/ssh_decorator/issues/11

Someone points out a backdoor installed in a python package. Someone else comes along to show how to write the backdoor more efficiently.

Quote

05-12-2018 , 08:46 PM

#1882

jmakin

banned

Join Date: Jan 2008 Posts: 30,120

python pros:

This is a wrapper that typechecks an argument passed into a function.

I need to write another wrapper @ReturnTypes that checks the return value. How would i go about this?

Code:

class AcceptTypes():
    def __init__(self, *args):
        self._args = args

    def __call__(self, f):
        def wrapped_f(*args):
            for i in range(len(self._args)):
                if type(args[i]) <> self._args[i]:
                    raise TypeError("Expecting %s got %s" % (str(self._args[i]), str(type(args[i]))))
            return f(*args)
        return wrapped_f
#
# The functions
#
@AcceptTypes(str)
def extract_words(path_to_file):
    with open(path_to_file) as f:
        str_data = f.read()
    pattern = re.compile('[\W_]+')
    word_list = pattern.sub(' ', str_data).lower().split()
    with open('./stop_words.txt') as f:
        stop_words = f.read().split(',')
    stop_words.extend(list(string.ascii_lowercase))
    return [w for w in word_list if not w in stop_words]

Quote

05-12-2018 , 09:19 PM

#1883

jmakin

banned

Join Date: Jan 2008 Posts: 30,120

I figured it out, but have no idea why it works:

Code:

class ReturnTypes():
        def __init__(self,*args):
                self._args = args
        def __call__(self, f):
                def wrapped(*args):
                        r = f(*args)

                        if type(r) <> self._args[0]:
                                raise TypeError("Expected %s got %s" % (str(self._args[0]), str(type(r))))
                        return r
                return wrapped

and put @ReturnTypes(<desired type>) in front of @AcceptTypes

particularly confused why if i remove "return r" the program no longer works. AcceptTypes calls and returns the function - why does return types "wrapped" have to?

Quote

05-13-2018 , 01:59 AM

#1884

RustyBrooks

Carpal \'Tunnel

Join Date: Feb 2006 Posts: 24,647

It's important to remember that

Code:

@mywrapper
def foo():
   something

is the same as

Code:

def foo():
    something

foo = mywrapper(foo)

And in your particular case, consider that your first wrapper does
return f(*args)

and your seconds does the same thing, but has to store and check the return value before returning, so it does
r = f(*args)
... check r
return r

So they're both returning the result of f(*args), the 2nd version just does an extra step with it.

Quote

05-13-2018 , 01:59 PM

#1885

jmakin

banned

Join Date: Jan 2008 Posts: 30,120

I tried removing the return f(*args) from accept types, and it no longer works if I do that either. They both have to return for this to work. That's what I'm a little confused about, why the original function seems to have to be returned twice, once in each of my __call__ methods

Quote

05-13-2018 , 03:10 PM

#1886

RustyBrooks

Carpal \'Tunnel

Join Date: Feb 2006 Posts: 24,647

I really don't like this example of yours - I hope it's not your introduction to wrappers. It's a case that is more complex than is usual, because the wrapper takes arguments so there's an extra layer of indirection. Let's try a simpler example.

Let's say I wanted to make a wrapper that catches any exceptions in a function and prints the error. Let's called it "printexc"

Code:

def printexc(f):
    def wrapper(*args, **kwargs):
        try:
            return f(*args, **kwargs)
        except Exception as e:
            print("An error occurred: {}".format(e))

    return wrapper

@printexc
def test1():
    return 1

@printexc
def test2():
    raise Exception("foo")


print("test1")
test1()

print()
print("test2")
test2()

This outputs

Code:

test1

test2
An error occurred: foo

See what's happening here? Wrapping test1 with printexc is the same as saying
test1 = printexc(test1)
printexc() is a function that returns the function "wrapper" right now. The code in "wrapper" doesn't run until you try to invoke test1(). When you do, it runs wrapper instead.

wrapper needs to return f(*args, **kwargs) because otherwise whatever has called test1 won't get it's return value.

If you had another wrapper called, like, printexc2 and you used both, like

Code:

@printexc
@prntexc2
def foo():
   ... do somethnig

Then this is the equivalent of

Code:

foo = printexc(printexc2(foo))

So when you invoke foo, its going to call the wrapper() returned by printexc, then it's going to call the wrapper() returned by printexc2, which is then going to call foo.

It's layered, so each layer has to call the function it wraps, and return the return value back up the stack.

Last edited by RustyBrooks; 05-13-2018 at 03:23 PM.

Quote

05-17-2018 , 01:04 PM

#1887

sixfour

should be called sevenfour

Join Date: Dec 2005 Posts: 74,766

Anyone here familiar with DAX? Trying to work out the most efficient way to code some stuff

Quote

05-17-2018 , 02:54 PM

#1888

jmakin

banned

Join Date: Jan 2008 Posts: 30,120

Quote:

Originally Posted by RustyBrooks

Code:

def printexc(f):
    def wrapper(*args, **kwargs):
        try:
            return f(*args, **kwargs)
        except Exception as e:
            print("An error occurred: {}".format(e))

    return wrapper

@printexc
def test1():
    return 1

@printexc
def test2():
    raise Exception("foo")


print("test1")
test1()

print()
print("test2")
test2()

This outputs

Code:

test1

test2
An error occurred: foo

Code:

@printexc
@prntexc2
def foo():
   ... do somethnig

Then this is the equivalent of

Code:

foo = printexc(printexc2(foo))

That makes sense. Thank you.

Quote

05-18-2018 , 06:18 PM

#1889

Loki

binary duo

Join Date: Nov 2015 Posts: 12,772

I dunno if this would be solvable via knapsack problem solutions or what, but I’m interested in figuring out a solution that’s basically the opposite of grep -c. Meaning, instead of entering a string and seeing how many times it’s in a file, I want to enter a number and see how many patterns are in a file that many times exactly and what those patterns are. This would be for about 10mb files or so.

Does this make sense? Would it take eternity to process a single file?

Quote

05-18-2018 , 10:28 PM

#1890

ChrisV

Carpal \'Tunnel

Join Date: Jul 2004 Posts: 40,336

You'd need a minimum length of the pattern and the algorithm might be a little tricky to write, but for 10MB files it shouldn't be too bad.

Quote

05-19-2018 , 01:54 PM

#1891

kerowo

lolcat

Join Date: Nov 2005 Posts: 37,190

Probably going to need a maximum length pattern as well, but it or something similar to it has probably been done by some cryptanalyst somewhere...

Like here: https://www.dcode.fr/frequency-analysis Well, the first step anyway, it will find all the times a pattern is in a file.

Here are the 4 letter patterns that show up in your post Loki:

Code:

↑↓	↑↓
WHAT	2
WOUL	2
UTIO	2
THIS	2
TMAN	1
ETHA	1
AFIL	1
YTIM	1
ESEX	1
EPAT	1
THOS	1
YAND	1
ACTL	1
REIN	1
RNSA	1
ERAN	1
NUMB	1
TERA	1
TOEN	1
DSEE	1
HOWM	1
TERN	1
ATTE	1
ANYP	1
WANT	1
ORAB	1
ERNI	1
KEET	1
ITTA	1
OULD	1
TYTO	1
PROC	1
LEFI	1
SING	1
ESSA	1
NSEW	1
KESE	1
OUTM	1
ILEI	1
DBEF	1
BFIL	1
ESOR	1
ISMA	1
ESTH	1
SODO	1
SARE	1
TIME	1
TEDI	1
ERES	1
MINT	1
BUTI	1
NFIG	1
URIN	1
NTHA	1
ASOL	1
GOUT	1
NSOR	1
MSOL	1
OLVA	1
DBES	1
NOIF	1
BLEV	1
IAKN	1
OBLE	1
CKPR	1
APSA	1
TSBA	1
SICA	1
ANDS	1
RING	1
GAST	1
ERIN	1
EEIN	1
GHOW	1
SITS	1
IDUN	1
MANY	1
FENT	1
EADO	1
POSI	1
HEOP	1
LLYT	1
TEOF	1
GREP	1
INST	1
NING	1
CMEA	1
INAF	1

Quote

05-19-2018 , 04:17 PM

#1892

Loki

binary duo

Join Date: Nov 2015 Posts: 12,772

i think i actually used that once at a capture-the-flag competition, hehe

The only problem is that I don't know the size of string i'm looking for. If I could build on what they've got and move from a given minimum to a maximum (with some exclusions) that would be pretty helpful... maybe.

appreciate the responses on this

Quote

05-20-2018 , 12:36 AM

#1893

jmakin

banned

Join Date: Jan 2008 Posts: 30,120

you need to know the max len, but just keep some type of hashmap and then iterate through it and output all the patterns where their freq = your N.

it's girthy, but for 10MB it's not that hard of a brute force solution. just set max len to like 100bytes or something.

Quote

05-20-2018 , 12:39 AM

#1894

jmakin

banned

Join Date: Jan 2008 Posts: 30,120

idk why but your problem reminds me of one i'm working on, the lempel ziv sliding window algorithm for file compression:

Lempel-Ziv Sliding Window

Quote

05-23-2018 , 02:20 AM

#1895

Barrin6

Carpal \'Tunnel

Join Date: Dec 2005 Posts: 6,947

Noob javascript question.

I have a function:

Code:

foo () { ... calls another webserver to do some computation .. }

foo() needs to return a value from that webserver. So obviously it has to be a synchronous request right? I can't change how foo() gets called here. I'm using XMLHttpRequest and everyone on the internet is saying it's deprecated. Even Google says the same.

How do fulfill foo() when it requires a synchronous return?

I'm doing a company coding challenge and rather than do the computation in javascript, I neglected to write my code in python and have this javascript code call my python server.

Quote

05-23-2018 , 02:43 AM

#1896

ChrisV

Carpal \'Tunnel

Join Date: Jul 2004 Posts: 40,336

Need a bit more information. It's not clear from what you said why the request has to be synchronous. Why can't you use a callback?

Quote

05-23-2018 , 03:08 AM

#1897

Barrin6

Carpal \'Tunnel

Join Date: Dec 2005 Posts: 6,947

Not sure how I can make it work with a callback. Correct me if I'm wrong, but generally callbacks are used to call another function or mutate some state.

foo() --> async call --> (what does foo() return??)

If foo() blocks then it's no longer async anymore.

I'm not the one calling foo() so I can't modify that person's code.

Quote

05-23-2018 , 03:25 AM

#1898

fredd-bird

Carpal \'Tunnel

Join Date: Aug 2007 Posts: 19,337

Instead of XMLHttpRequest, I would point you towards fetch as a first step (https://developers.google.com/web/up...ction-to-fetch).

Then I think you'll want to look into async/await (https://javascript.info/async-await, https://medium.com/@kvosswinkel/is-j...e-7aa9dd8f3bfb funfunfunction video at the end is solid too). Adding async out in front of the function declaration will allow you to use await, which makes it act like synchronous request.

Code:

// fetch
function foo() {
    return fetch('https://api.twoplustwo.com/')
        .then(response => return response.json())
}

// async/await
async function foo() {
    const response = await fetch('https://api.twoplustwo.com/')
    const data = await response.json()
    return data
}