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how can I find python 3 codes only on github?

Is there a way to know which codes on github are in python 3? So far, I haven't any mentionned.
Tks

Very simply:
Yes, you can find Python3 code.
No, you cannot do so effectively.
Code on GitHub is not identified by language and version -- obviously, since you would have found that in your investigations before coding. Yes, you can generally determine the language of a code file, but only with detailed examination -- you would almost need to pass the file to a Python compiler and reject any with syntax errors. This is not an effective process.
You can reduce the search somewhat by gleaning *.py files and then look for frequent, 3-specific features, such as all print commands using parentheses (coding style in Python 2, mandated in Python 3). This merely reduces the problem; it does not give you a good request mechanism.

How to protect my Python code before distribution?

I have written a python code which takes an input data file, performs some processing on the data and writes another data file as output.
I should distribute my code now but the users should not see the source code but be able to just giving the input and getting the output!
I have never done this before.
I would appreciate any advice on how to achieve this in the easiest way.
Thanks a lot in advance

As Python is an interpreted language by design; and as it compiles code to a bytecode (- which doesn't help the fact you're trying to conceal it, as bytecodes are easier to reverse -) there's no real secure way to hide your source code whereby it is not recoverable, as is true for any programming language, really.
Initially, if you'd wanted to work with a language that can't be so easily reversed- you should've gone for a more native language which compiles directly to the underlying architecture's machine code which is significantly harder to reproduce in the original language let alone read due to neat compiler optimizations, the overhead given by CISC et cetera.
However, some libraries that do convert your source code into an executable format (by packing the Python interpreter and the bytecode alongside it) can be used such as:
cx_Freeze - for freezing any code >=Python 2.7 for any platform, allegedly.
PyInstaller - for freezing general purpose code, it does state additionally that it works with third-party libraries.
py2exe -for freezing code into Windows-only executable format.
Or you might consider a substitute for this, which is code obfuscation which still allows the user to read the source code however make it near-to-impossible to read.
However, an issue brought up with this is that, it'd be harder for code addition as bad code obfuscation techniques could make the code static. Also, on the latter case, the code could have overhead brought by redundant code meant to fool or trick the user into thinking the code is doing something which it is not.
Also in general it negates the standard practice of open-source which is what Python loves to do and support.
So to really conclude, if you don't want to read everything above; the first thing you did wrong was choose Python for this, a language that supports open source and is open source as well. Thus to mitigate the issue you should either reconsider the language, or follow the references above to links to modules which might help aide basic source code concealment.

Firstly, as Python is an interpreted language, I think you cannot completely protect your Python code, .pyc files can be uncompiled to get back .py files (using uncompyle6 for example).
So the only thing you can do is make it very hard to read.
I recommend to have a look at code obfuscation, which consists in making your code unreadable by changing variables/function names, removing comments and docstrings, removing useless spaces, etc. Pyminifier does that kind of things.
You can also write your own obfuscation script.
Then you can also turn your program into a single executable (using pyinstaller for example). I am pretty sure there is a way to get .py files back from the executable, but it just makes it harder. Also beware of cross-platform compatibility when making an executable.

Going through above responses, my understanding is that some of the strategies mentioned may not work if your client wants to execute your protected script along with other unprotected scripts.
One other option is to encrypt your script and then use an interpreter that can decrypt and execute it. It too has some limitations.
ipepycrypter is a suite that helps protect python scripts. This is accomplished by hiding script implementation through encryption. The encrypted script is executed by modifed python interpreter. ipepycrypter consists of encryption tool ipepycrypt and python interpreter ipepython.
More information is available at https://ipencrypter.com/user-guides/ipepycrypter/

One other option, of course, is to expose the functionality over the web, so that the user can interact through the browser without ever having access to the actual code.

There are several tools which compile Python code into either (a) compiled modules usable with CPython, or (b) a self-contained executable.
https://cython.org/ is the best known, and probably? oldest, and it only takes a very small amount of effort to prepare a traditional Python package so that it can be compiled with Cython.
http://numba.pydata.org/ and https://pythran.readthedocs.io/ can also be used in this way, to produce Python compiled modules such that the source doesnt need to be distributed, and it will be very difficult to decompile the distributable back into usable source code.
https://mypyc.readthedocs.io is newer player, an offshoot of the mypy toolkit.
Nuitka is the most advanced at creating a self-contained executable. https://github.com/Nuitka/Nuitka/issues/392#issuecomment-833396517 shows that it is very hard to de-compile code once it has passed through Nuitka.
https://github.com/indygreg/PyOxidizer is another tool worth considering, as it creates a self-contained executable of all the needed packages. By default, only basic IP protection is provided, in that the packages inside it are not trivial to inspect. However for someone with a bit of knowledge of the tool, it is trivial to see the packages enclosed within the binary. However it is possible to add custom module loaders, so that the "modules" in the binary can be stored in unintelligible formats.
Finally, there are many Python to C/go/rust/etc transpilers, however these will very likely not be usable except for small subsets of the language (e.g. will 3/0 throw the appropriate exception in the target language?), and likely will only support a very limited subset of the standard library, and are unlikely to support any imports of packages beyond the standard library. One example is https://github.com/py2many/py2many , but a search for "Python transpiler" will give you many to consider.

Need Python guide on Windows

I am trying to set up Python on Windows 7. I haven't used this language before so it seems strange to me.
I've downloaded lastest Python release 3.2.2 from official site and upadate path variable.
However I still can't even run simplest program ever like this :
print 'Hello, world!'
It says that there is a syntax error and the last character ' is highlighted with red.
I don't know if my path variable has been set properly. Here is where I installed Python :
C:\Software\Python32
So I added such a variable : var name = PYTHONPATH , var value = C:\Software\Python32\Lib
Is there something with auto-completion and with errors/warnings details ( which line, hint what can be wrong ), for example like Eclipse or NetBeans OR should I use this installed Python IDLE GUI for delevoping or stuff like NotePad++ ?
Actually what is this Python shell for ? - I know that I can type in some arithmetic operations here and I will get results, but is it used for something more advanced ? ( Is it used when I am writting something bigger ? )
Could someone describe simple way to write and execute a program ( or script I a total beginner so I don't really know what it is going on here ) ?

In Python 3.2 you have to use print in the below manner. The parentheses are mandatory. (print became a function in Python 3)
print('Hello World')

As Venk stated, the print statement in Python 2.x has been replaced with print() in 3.x, so your statement should read
print('Hello World')
Since you're new, here some things you should know about Python versions:
Python currently comes in two flavors: Python 2.x and Python 3.x.
Python 2.x has been in development since the late '90s, so most existing codebases, frameworks, and libraries are written in this flavor of Python. Each successive version is backwards compatible, so, for example, all code written in Python 2.4 can be run with Python 2.4+. Its current revision is 2.7.2, which was released last year.
Python 3.x is considered the "future" of Python, and purposefully breaks a lot of the conventions, such as the print statement, in favor of a clearer, more explicit language. Most libraries are working to port over to Python 3.x, but since there are extensive changes in the structure of the language, most library maintainers have not yet been able to release a Python 3.x compatible version with the full features of the Python 2.x version of the library.
If you're developing now, you should learn Python 2.x; otherwise, it's recommended you learn Python 3.x.
To answer your other questions:
Python's native IDLE is an excellent IDE, but if you're looking for something more advanced, you may want to try out Eclipse's PyDev extension or PyCharm. I personally prefer PyCharm, since it doesn't keep giving me errors when I'm importing/using nonstandard Python libraries/frameworks.
In addition, Python's shell is used to interpret Python scripts (in the background) and for interactive interpreting (i.e., quick and dirty testing), and can execute code you type into it. The latter, however, is not recommended, as a single syntax error in multiple lines of code can force you to retype all the lines to fix a single bug.
Furthermore, all Python scripts end in .py, so if you can see the file extensions, you can convert a text file into a Python script, and run from shell by typing python path/to/file.py. Note, however, that you still have to write a valid Python script, or it will not run.

I suggest A Byte of Python. It'll take you through install, REPL, syntax, and the std library.

The python shell is for entering code interactively.
Try the following: http://docs.python.org/tutorial/

I've been using Python on Windows 7 for 3 years now, and I strongly recommend Notepad++ as your editor/interpreter. It is ideal for people who want to play around with the language and are learning. Notepad++ can be customized for almost any language and is free for Windows. Follow this link
and take a look at how to conveniently use Notepad++ to execute Python scripts.

Which Python IDE can run my script line-by-line?

I wouldn't call myself programmer, but I've started learning Python recently and really enjoy it.
I mainly use it for small tasks so far - scripting, text processing, KML generation and ArcGIS.
From my experience with R (working with excellent Notepad++ and NppToR combo) I usually try to work with my scripts line by line (or region by region) in order to understand what each step of my script is doing.. and to check results on the fly.
My question: is there and IDE (or editor?) for Windows that lets you evaluate single line of Python script?
I have seen quite a lot of discussion regarding IDEs in Python context.. but havent stubled upon this specific question so far.
Thanks for help!

If you like R's layout. I highly recommend trying out Spyder. If you are using windows, try out Python(x,y). It is a package with a few different editors and a lot of common extra modules like scipy and numpy.

The only one I've had success with is Eclipse with Pydev

It's not an IDE, but you can use pdb to debug and step through your Python code. I know Emacs has built in support for it, but not so much about other editors (or IDEs) that will run in Windows.

If you are on Windows, give Pyscripter a try -- it offers comprehensive, step-through debugging, which will let you examine the state of your variables at each step of your code.

PyCharm from JetBrains has a very nice debugger that you can step through code with.
Django and console integration built in.

Rodeo seems to be new contender on the IDE market and the docs indicate that running lines of code is possible. I also have to admit it looks and behaves pretty good so far!

WingIDE, I've been using it successfully for over a year, and very pleased with it.

I use Notepad++ for most of my Windows based Python development and for debugging I use Winpdb. It's a cross platform GUI based debugger. You can actually setup a keyboard shortcut in Notepad++ to launch the debugger on your current script:
To do this go to "Run" -> "Run ..." in the menu and enter the following, making sure the path points to your winpdb_.pyw file:
C:\python26\Scripts\winpdb_.pyw "$(FULL_CURRENT_PATH)"
Then choose "Save..." and pick a shortcut that you wish to use to launch the debugger.
PS: You can also setup a shortcut to execute your python scripts similarly using this string instead:
C:\python26\python.exe "$(FULL_CURRENT_PATH)"

The upcoming RStudio 1.2 is so good that you have to try to write some python with it. 🙌

I would plump for EMACS all round.
If you're looking for a function to run code line by line (or a region if you have one highlighted), try adding this to your .emacs (I'm using python.el and Pymacs):
;; send current line to *Python
(defun my-python-send-region (&optional beg end)
(interactive)
(let ((beg (cond (beg beg)
((region-active-p)
(region-beginning))
(t (line-beginning-position))))
(end (cond (end end)
((region-active-p)
(copy-marker (region-end)))
(t (line-end-position)))))
(python-shell-send-region beg end)))
(add-hook 'python-mode-hook
'(lambda()
(local-set-key [(shift return)] 'my-python-send-region)))
I've bound it to [shift-Return]. This is borrowed from here. There's a similar keybinding for running .R files line by line here. I find both handy.

I like vim-ipython. With it I can <ctrl>+s to run a specific line. Or several lines selected on visual modes. Take a look at this video demo.

Visual Studio and PTVS: http://www.hanselman.com/blog/OneOfMicrosoftsBestKeptSecretsPythonToolsForVisualStudioPTVS.aspx
(There is also a REPL inside VS)

The Pythonwin IDE has a built-in debugger at lets you step through your code, inspect variables, etc.
http://starship.python.net/crew/mhammond/win32/Downloads.html
http://sourceforge.net/projects/pywin32/
The package also includes a bunch of other utility classes and modules that are very useful when writing Python code for Windows (interfacing with COM, etc.).
It's also discussed in the O'Reilly book Python Programming On Win32 by Mark Hammond.

Take the hint: The basic Python Read-Execute-Print-Loop (REPL) must work.
Want Evidence?
Here it is: The IDE's don't offer much of an alternative. If REPL wasn't effective, there's be lots of very cool alternatives. Since REPL is so effective, there are few alternatives.
Note that languages like Java must have a step-by-step debugger because there's no REPL.
Here's the other hint.
If you design your code well, you can import your libraries of functions and classes and exercise them in REPL model. Many, many Python packages are documented by exercising the package at the REPL level and copying the interactions.
The Django documentation -- as one example -- has a lot of interactive sessions that demonstrate how the parts work together at the REPL prompt.
This isn't very GUI. There's little pointing and clicking. But it seems to be effective.

You need to set the keyboard shortcut for "run selection" in
Tools > Preferences > Keyboard shortcuts
Then, select the line and hit the "run selection" shortcut

Light Table was doing that for me, unfortunately it is discontinued:
INLINE EVALUTION No more printing to the console in order to view your
results. Simply evaluate your code and the results will be displayed
inline.

Can i take package of cpython?

I used cpython api to load py from C/C++.
But, if i want not setup cpython in client, can I take package dll of cpython in my program?
How to do that?

Installer-builders like PyInstaller (cross-platform) and py2exe (Windows only) basically do that job for you in a general way, except that the executable at the heart of the produced package is their own instead of yours.
But basically, you can imitate their behavior in terms of setting up a .zip file with all the Python library modules you need (or just zip up everything in the standard python library if you want to allow python code running form your app to import anything from there), and follow the simple advice in the Embedding Python in Another Application section of the Python docs.
Note that embedding Python equals extending Python plus a little bit of code to initialize and finalize the interpreter itself and a little bit of packaging as I just mentioned; if you've never writted Python extensions I would suggest practicing that first since it's the most substantial part of the task (not all that hard with helpers such as boost python, but more work if you choose to do it as the "bare C" level instead).

You don't need to setup Python to embed it in applications. The core of the Python interpreter is available as a shared library which you can dynamically load in your application and distribute with it.
Read on embedding Python in the official docs. Also, this article seems nice and comprehensive for Linux. For Windows, read the notes here.
Here's another SO question that discusses this issue.

The Python license is probably hard to understand for a non-lawyer, non-native English speaker. So yes, you can redistribute the unmodified DLL as it contains the copyright notice within it.
It would be polite to give credit like "This program contains the Python Language Interpreter version X.XX http://python.org for more information" or similar somewhere in the program or documentation.