How can I reference an input twice in a one line code?
Ex:
my_word=input()
print("hey" if my_word==my_word else "bye")
You are only referencing it once right now, so this is easy:
print("hey" if input().isdigit() else "bye")
Though you could argue that this line of code does too much, and may be difficult to maintain. Breaking it into two lines makes maintenance easier, and for example it also allows you to set a breakpoint on the print line and inspect the value in my_word if you wanted to.
For academic reasons, here is one possible solution to evaluating an expression once but using it multiple times in one statement: list comprehension. (This is a terrible, terrible idea, and you shouldn't do this. I mean it.)
[print(i if i.isdigit() else "bye") for i in (input(),)]
Related
I've been going through a course and trying to find ways to shorten my code. I had this assignment to open a text file, split it, then add all of the unique values to a list, then finally sort it. I passed the assignment, but I have been trying to shorten it to learn some ways to apply any shortening concepts to future codes. The main issues I keep running into is trying to make the opened file into strings to turn them into lists to append and such without read(). If I don't used read() I get back TextIO errors. I tried looking into it but what I found involved importing os and doing some other funky stuff, which seems like it would take more time.
So if anyone would mind giving me tips to more effectively code this that are beginner friendly I would be appreciative.
romeo = open('romeo').read()
mylist = list()
for line in romeo.split() :
if line not in mylist:
mylist.append(line)
mylist.sort()
print(mylist)
I saw that set() is pretty good for unique values, but then I don't think I can sort it. Then trying flip flop between a list and set would seem wacky. I tried those swanky one line for loop boys, but couldn't get it to work. like for line not in mylist : mylist.append(line) I know that's not how to do it or even close, but I don't know how to convey what I mean.
So to iterate:
1. How to get the same result without read() / getting around textIO
2. How to write this code in a more stream lined way.
I'm new to the site and coding, so hopefully I didn't trigger anyone.
I would like to change the behavior of menhir's output in follwoing way:
I want it to look up all grammatical alternatives if it finds any, and put them in a list and get me back this ambigouus interpretation. It shall not reduce conflicts, just store them.
In the source code of menhir, it seems to me, that I have to look in "Engine.ml". The resultant syntactically determined token comes in a variant type item "Accepted v" as a state of a checkpoint of the grammatical automaton. This content is found by a function "accept env prod" before, that is part of a bundle of recursive functions, that change the states.
Do you have a tip, how I could change these functions to put all the possible results in the list here and proceed as if nothing happened? Or do you think, that this wont work anyway?
Thanks.
What you are looking for is a GLR parser generator (G is for generalized). Menhir is not such tool, and I doubt you could modify it easily to do what you want.
However, there is another tool that does exactly what you want: dypgen.
Lets say that there is a function in my Delphi app:
MsgBox
and there is a string which has MsgBox in it.
I know what most of you are going to say is that its possible, but I think it is possible because I opened the compiled exe(compiled using delphi XE2) using a Resource Editor, and that resource editor was built for Delphi. In that, I could see most of the code I wrote, as I wrote it. So since the variables names, function names etc aren't changed during compile, there should a way to execute the functions from a string, but how? Any help will be appreciated.
EDIT:
What I want to do is to create a simple interpreter/scripting engine. And this is how its supposed to work:
There are two files, scr.txt and arg.txt
scr.txt contains:
msg_show
0
arg.txt contains:
"Message"
And now let me explain what that 0 is:
First, scr.txt's first line is function name
second line tells that at which line its arguments are in the arg.txt, i.e 0 tells that "Message" is the argument for msg_show.
I hope my question is now clear.
I want to make a simple scripting engine.
In order to execute arbitrary code stored as text, you need a compiler or an interpreter. Either you need to write one yourself, or embed one that already exists. Realistically, the latter option is your best option. There are a number available but in my view it's hard to look past dwscript.
I think I've already solved my problem! The answer is in this question's first answer.
EDIT:
But with that, as for a workaround of the problem mentioned in first comment, I have a very easy solution.
You don't need to pass all the arguments/parameters to it. Just take my example:
You have two files, as mentioned in the question. Now you need to execute the files. It is as simple as that:
read the first line of scr.txt
check if it's a function. If not, skip the line
If yes, read the next line which tells the index where it's arguments are in arg.txt
pass on the index(an integer) to the "Call" function.
Now to the function which has to be executed, it should know how many arguments it needs. i.e 2
Lets say that the function is "Sum(a,b : integer)".It needs 2 arguments
Now let the function read the two arguments from arg.txt.
And its done!
I hope it will help you all.
And I can get some rep :)
Consider the following sample codes:
1.Sample
var IsAdminUser = (User.Privileges == AdminPrivileges)
? 'yes'
: 'no';
console.log(IsAdminUser);
2.Sample
var IsAdminUser = (User.Privileges == AdminPrivileges)?'yes': 'no';
console.log(IsAdminUser);
The 2nd sample I am very comfortable with & I code in that style, but it was told that its wrong way of doing without any supportive reasons.
Why is it recommended not to use a single line ternary operator in Node.js?
Can anyone put some light on the reason why it is so?
Advance Thanks for great help.
With all coding standards, they are generally for readability and maintainability. My guess is the author finds it more readable on separate lines. The compiler / interpreter for your language will handle it all the same. As long as you / your project have a set standard and stick to it, you'll be fine. I recommend that the standards be worked on or at least reviewed by everyone on the project before casting them in stone. I think that if you're breaking it up on separate lines like that, you may as well define an if/else conditional block and use that.
Be wary of coding standards rules that do not have a justification.
Personally, I do not like the ternary operator as it feels unnatural to me and I always have to read the line a few times to understand what it's doing. I find separate if/else blocks easier for me to read. Personal preference of course.
It is in fact wrong to put the ? on a new line; even though it doesn’t hurt in practice.
The reason is a JS feature called “Automatic Semicolon Insertion”. When a var statement ends with a newline (without a trailing comma, which would indicate that more declarations are to follow), your JS interpreter should automatically insert a semicolon.
This semicolon would have the effect that IsAdminUser is assigned a boolean value (namely the result of User.Privileges == AdminPrivileges). After that, a new (invalid) expression would start with the question mark of what you think is a ternary operator.
As mentioned, most JS interpreters are smart enough to recognize that you have a newline where you shouldn’t have one, and implicitely fix your ternary operator. And, when minifying your script, the newline is removed anyway.
So, no problem in practice, but you’re relying on an implicit fix of common JS engines. It’s better to write the ternary operator like this:
var foo = bar ? "yes" : "no";
Or, for larger expressions:
var foo = bar ?
"The operation was successful" : "The operation has failed.";
Or even:
var foo = bar ?
"Congratulations, the operation was a total success!" :
"Oh, no! The operation has horribly failed!";
I completely disagree with the person who made this recommendation. The ternary operator is a standard feature of all 'C' style languages (C,C++,Java,C#,Javascript etc.), and most developers who code in these languages are completely comfortable with the single line version.
The first version just looks weird to me. If I was maintaining code and saw this, I would correct it back to a single line.
If you want verbose, use if-else. If you want neat and compact use a ternary.
My guess is the person who made this recommendation simply wasn't very familiar with the operator, so found it confusing.
Because it's easier on the eye and easier to read. It's much easier to see what your first snippet is doing at a glance - I don't even have to read to the end of a line. I can simply look at one spot and immediately know what values IsAdminUser will have for what conditions. Much the same reason as why you wouldn't write an entire if/else block on one line.
Remember that these are style conventions and are not necessarily backed up by objective (or technical) reasoning.
The reason for having ? and : on separate lines is so that it's easier to figure out what changed if your source control has a line-by-line comparison.
If you've just changed the stuff between the ? and : and everything is on a single line, the entire line can be marked as changed (based on your comparison tool).
I have seen a lot of C/C++ based solutions to this problem where we have to write a program that upon execution prints its own source.
some solutions --
http://www.cprogramming.com/challenges/solutions/self_print.html
Quine Page solution in many languages
There are many more solutions on the net, each different from the other. I wonder how do we approach to such a problem, what goes inside the mind of the one who solves it. Lend me some insights into this problem... While solutions in interpreted languages like perl, php, ruby, etc might be easy... i would like to know how does one go about designing it in compiled languages...
Aside from cheating¹ there is no difference between compiled and interpreted languages.
The generic approach to quines is quite easy. First, whatever the program looks like, at some point it has to print something:
print ...
However, what should it print? Itself. So it needs to print the "print" command:
print "print ..."
What should it print next? Well, in the mean time the program grew, so it needs to print the string starting with "print", too:
print "print \"print ...\""
Now the program grew again, so there's again more to print:
print "print \"print \\\"...\\\"\""
And so on.
With every added code there's more code to print.
This approach is getting nowhere,
but it reveals an interesting pattern:
The string "print \"" is repeated over and over again.
It would be nice to put the repeating part
into a variable:
a = "print \""
print a
However, the program just changed,
so we need to adjust a:
a = "a = ...\nprint a"
print a
When we now try to fill in the "...",
we run into the same problems as before.
Ultimately, we want to write something like this:
a = "a = " + (quoted contents of a) + "\nprint a"
print a
But that is not possible,
because even if we had such a function quoted() for quoting,
there's still the problem that we define a in terms of itself:
a = "a = " + quoted(a) + "\nprint a"
print a
So the only thing we can do is putting a place holder into a:
a = "a = #\nprint a"
print a
And that's the whole trick!
Anything else is now clear.
Simply replace the place holder
with the quoted contents of a:
a = "a = #\nprint a"
print a.replace("#", quoted(a))
Since we have changed the code,
we need to adjust the string:
a = "a = #\nprint a.replace(\"#\", quoted(a))"
print a.replace("#", quoted(a))
And that's it!
All quines in all languages work that way
(except the cheating ones).
Well, you should ensure that you replace only
the first occurence of the place holder.
And if you use a second place holder,
you can avoid needing to quote the string.
But those are minor issues
and easy to solve.
If fact, the realization of quoted() and replace()
are the only details in which the various quines really differ.
¹ by making the program read its source file
There are a couple of different strategies to writing quines. The obvious one is to just write code that opens the code and prints it out. But the more interesting ones involve language features that allow for self-embedding, like the %s-style printf feature in many languages. You have to figure out how to embed something so that it ends up resolving to the request to be embedded. I suspect, like palindromes, a lot of trial and error is involved.
The usual approach (when you can't cheat*) is to write something that encodes its source in a string constant, then prints out that constant twice: Once as a string literal, and once as code. That gets around the "every time I write a line of code, I have to write another to print it out!" problem.
'Cheating' includes:
- Using an interpreted language and simply loading the source and printing it
- 0-byte long files, which are valid in some languages, such as C.
For fun, I came up with one in Scheme, which I was pretty proud of for about 5 minutes until I discovered has been discovered before. Anyways, there's a slight modification to the "rules" of the game to better count for the duality of data and code in Lisp: instead of printing out the source of the program, it's an S-expression that returns itself:
((lambda (x) (list x `',x)) '(lambda (x) (list x `',x)))
The one on Wikipedia has the same concept, but with a slightly different (more verbose) mechanism for quoting. I like mine better though.
One idea to think about encoding and how to give something a double meaning so that it can be used to output something in a couple of forms. There is also the cavaet that this type of problem comes with restrictions to make it harder as without any rules other than the program output itself, the empty program is a solution.
How about actually reading and printing your source code? Its not difficult at all!! Heres one in php:
<?php
{
header("Content-Type: text/plain");
$f=fopen("5.php","r");
while(!feof($f))
{
echo fgetc($f);
}
fclose($f);
}
?>
In python, you can write:
s='c=chr(39);print"s="+c+s+c+";"+s';c=chr(39);print"s="+c+s+c+";"+s
inspired from this self printing pseudo-code:
Print the following line twice, the second time with quotes.
"Print the following line twice, the second time with quotes."
I've done a AS3 example for those interested in this
var program = "var program = #; function main(){trace(program.replace('#',
String.fromCharCode(34) + program + String.fromCharCode(34)))} main()";
function main(){
trace(program.replace('#', String.fromCharCode(34) + program + String.fromCharCode(34)))
}
main()
In bash it is really easy
touch test; chmod oug+x test; ./test
Empty file, Empty output
In ruby:
puts File.read(_ _ FILE _ _)