Develop Reference

(python - cpp) - How to split the c++ codes while writing a lexical analyzer in python?

I wrote a lexical analyzer for cpp codes in python, but the problem is when I use input.split(" ") it won't recognize codes like x=2 or function() as three different tokens unless I add an space between them manually, like: x = 2 .
also it fails to recognize the tokens at the beginning of each line.
(if i add spaces between each two tokens and also at the beginning of each line, my code works correctly)
I tried splitting the code first by lines then by space but it got complicated and still I wasn't able to solve the first problem.
Also I thought about splitting it by operators, yet I couldn't actually implement it. plus I need the operators to be recognized as tokens as well, so this might not be a good idea.
I would appreciate it if anyone could give any solution or suggestion, Thank You.
f=open("code.txt")
input=f.read()
input=input.split(" ")
f=open("code.txt")
input=f.read()
input1=input.split("\n")
for var in input1:
var=var.split(" ")

Obviously, if you try to have success splitting such an expression like x=2 and also x = 2... it seems pretty obvious that isn't going to work.
What you are looking is for a solution that works with both right?
Basic solution is to use an and operator, and use the conditions that you need to parse. Note that this solution isn't scalable, neither fits into the category of good practices, but it can help you to figure out better but harder solutions.
if input.split(' ') and input.split('='):
An intermediate solution would be to use regex.
Regex isn't an easy topic, but you can checkout online documentation, and then you have wonderful online tools to check your regex codes.
Regex 101
The last one, would be to convert your input data into an AST, which stands for abstract syntax tree. This is the technique employed by C++ compilers like, for example, Clang.
This last one is a real hard topic, so for figure out a basic lexer, probably will be really time consuming, but maybe it could fit your needs.

The usual approach is to scan the incoming text from left to right. At each character position, the lexical analyser selects the longest string which fits some pattern for a "lexeme", which is either a token or ignored input (whitespace and comments, for example). Then the scan continues at the next character.
Lexical patterns are often described using regular expressions, but the standard regular expression module re is not as much help as it could be for this procedure, because it does not have the facility of checking multiple regular expressions in parallel. (And neither does the possible future replacement, the regex module.) Or, more precisely, the library can check multiple expressions in parallel (using alternation syntax, (...|...|...)), but it lacks an interface which can report which of the alternatives was matched. [Note 1]. So it would be necessary to try every possible pattern one at a time and select whichever one turns out to have the longest match.
Note that the matches are always anchored at the current input point; the lexical analyser does not search for a matching pattern. Every input character becomes part of some lexeme, even if that lexeme is ignored, and lexemes do not overlap.
You can write such an analyser by hand for a simple language, but C++ is hardly a simple language. Hand-built lexical analysers most certainly exist, but all the ones I've seen are thousands of lines of not very readable code. So it's usually easier to build an analyzer automatically using software designed for that purpose. These have been around for a long time -- Lex was written almost 50 years ago, for example -- and if you are planning on writing more than one lexical analyser, you would be well advised to investigate some of the available tools.
Notes
The PCRE2 and Oniguruma regex libraries provide a "callout" feature which I believe could be used for this purpose. I haven't actually seen it used in lexical analysis, but it's a fairly recent addition, particularly for Oniguruma, and as far as I can see, the Python bindings for those two libraries do not wrap the callout feature. (Although, as usual with Python bindings to C libraries, documentation is almost non-existent, so I can't say for certain.)

Convert SAS Compged function to Python

For project requirements, I am converting all the SAS codes to python, I got stuck where for 2 string matching, SAS inbuilt COMPGED function is used. I need the same score so need to convert it into Python code rather than using other libraries like fuzzywuzzy.
Please help if possible, just need some starter code to understand how to build it.
COMPGED

Getting exact match is going to be extremely complex. You will need to produce your own implementation of the generalised edit distance.
A good starting point might be here:
https://www.python-course.eu/levenshtein_distance.php

Change Regular Expression to NFA and then to DFA in python using Thomsons Construction and Subset Construction

I need to convert the Regular Expression inputted having alphabets = {a,b} and the operations to be included are Concatenation, Union, Kleene Closure, somewhat of the form (a|b)*abab.
Would someone suggest how I can implement it in Python? Is there any function or so in Python for this, and if so, please tell me how to use it. If not, then please tell me how to code it from scratch. I have been trying to figure out how to write an effective code for this, but each time I have an error or I have wrong output.

The Answer to the above question has been put on github. The link for the same is =>
Compilers

Matlab function equivalent for Python (Flood Fill)

Quick question, I'm looking for a python function that performs the equivalent job that matlab's imfill.m does. I realize that python has openCV but I have been unable to get that to work properly and am trying to find a substitute for it. The part of imfill that I'm trying to replicate is the 'holes' part of it.
I have a mask that I've generated but I'm trying to fill in all regions that are surrounded by 'land' and leave only the water regions unfilled in.
If this isn't clear enough please let me know and I can try and be more specific. Thank you for your time.

I was able to find a function within scipy that performed similar to what imfill does. It's called binary_fill_holes and it can be found here for anyone that is having the same problem as myself.
Although I can't take full/any real credit for finding it since it was answered here to one of my other questions PIL Plus/imToolkit replacements by unutbu.

Python coding test problem for interviews [closed]

Closed. This question needs to be more focused. It is not currently accepting answers.
Want to improve this question? Update the question so it focuses on one problem only by editing this post.
Closed 6 years ago.
Improve this question
I'm trying to come up with a good coding problem to ask interview candidates to solve with Python.
They'll have an hour to work on the problem, with an IDE and access to documentation (we don't care what people have memorized).
I'm not looking for a tough algorithmic problem - there are other sections of the interview where we do that kind of thing. The point of this section is to sit and watch them actually write code. So it should be something that makes them use just the data structures which are the everyday tools of the application developer - lists, hashtables (dictionaries in Python), etc, to solve a quasi-realistic task. They shouldn't be blocked completely if they can't think of something really clever.
We have a problem which we use for Java coding tests, which involves reading a file and doing a little processing on the contents. It works well with candidates who are familiar with Java (or even C++). But we're running into a number of candidates who just don't know Java or C++ or C# or anything like that, but do know Python or Ruby. Which shouldn't exclude them, but leaves us with a dilemma: On the one hand, we don't learn much from watching someone struggle with the basics of a totally unfamiliar language. On the other hand, the problem we use for Java turns out to be pretty trivial in Python (or Ruby, etc) - anyone halfway competent can do it in 15 minutes. So, I'm trying to come up with something better.
Surprisingly, Google doesn't show me anyone doing something like this, unless I'm just too dumb to enter the obvious search term. The best idea I've come up with involves scheduling workers to time slots, but it's maybe a little too open-ended. Have you run into a good example? Or a bad one? Or do you just have an idea?

I've asked candidates to write code to implement bowling scoring before, which is readily comprehensible but contains enough wrinkles that most people have to iterate their approach a couple times to cover all the edge cases.
A lot of the problems at http://www.streamtech.nl/site/problem+set, which are taken from ACM competitions, are also suitable for your use. I used them to familiarize myself with python syntax and language features. A lot amount to straightforward application of standard data structures; some are more focused on algorithmic issues. If you sort through them I'm sure you'll find several that fit your needs.

I can recommend to you Checkio.org

You can always just give them a few more questions on top of the Java one, like ask them to do the Java task, then ask them to define a class, then ask them to do FizzBuzz. That should be about as rigorous as your Java task.
Don't be afraid to ask a series of questions. Maybe you can even ask them to write a few one-liners to make sure they get the finer points of Python (write a list comprehension, how do you define a lambda, etc.)

Here's a question I answered on SO recently that might be the start of something suitable:
Given a string "O João foi almoçar :)
.", split it into a list of words.
You must strip all punctuation except
for emoticons. Result for example:
['O','João', 'foi', 'almoçar', ':)']
I've tidied up the question a bit. See the original linked above along with my answer. It tests a number of things, and there are different ways of tackling the problem. They can also get a half-solution out that first disregards the emoticons and punctuation aspect. Just finding the emoticons is another sub-problem that can be solved separately. And so on...
You could extend it to asking about emoticons adjacent to other punctuation, adjacent emoticons, overlapping emoticons, defining emoticons in :) form but also searching for those of the form :-). You could also turn it into a frequency count problem instead of just splitting to somewhat line up with your Java question.
I also suggest searching through the python+interview-questions questions posted on SO. There are some good ones, and you may even want to broaden your search to skim all interview-questions posts if you have time.

I don't know about Python specifically, but I found that interview questions which involve recursion are a very effective filter. I have asked candidates to produce all the permutations of a string (and think about how to test it), and I have been asked to pseudo-code the Longest Common Subsequence.