What happens behind the scenes when we invoke the python prompt?
I am more interested in understanding how do the methods/functions like print, import and the likes load up in the interpreter?
EDIT: Some clarification on my question:
When we type python on our unix prompt/windows console and Hit enter, what are the libraries that get loaded. My specific interest is as to how the keywords like print and import are made available to the user.
Like you , I am very interested by the underlying mechanisms of Python.
I think you'll love this series:
http://tech.blog.aknin.name/category/my-projects/pythons-innards/
There are too many levels to that question. Here's a very rough sketch.
There's the whole C-level interpreter initialization, a bunch of in-the-interpreter tasks, reading the environment and options, customization of the interpreter session. All that defines what you see when you run python.
I know there's a good description of the whole process somewhere.
Related
So, I recently made a Python program that I want to send to someone with them being able to execute it, but not read the code I have typed in it. Any ideas how to do it?
BTW, I want it to be irreversible
In short, here are my Parameters:
Should remain a Python file
Can't be reversed
Code should not be readable
Should still have the ability to be run
The criteria you've posted are inconsistent.
Python is an interpreted language. The entity running the language (i.e. Python interpreter) is reading your code and executing it, line by line. If you wrap it up to send to someone, their Python interpreter must have read permissions on the file, whether it's source code or "compiled" Python (which is easily decompiled into equivalent source code).
If we take a wider interpretation of "send to someone", there may be a business solution that serves your needs. You would provide your functionality, rather than the code: deploy it as a service from some available server: your own, or rented space. To do this, you instead provide an interface to your functionality.
If this fulfills your needs, you now have your next research topic.
I am developing a small program which I want to give to my younger friends to introduce them to the bare minimum basics of programming using Python.
In it, I want to add functionality to output the line of code that is being executed, as it is being executed, to the console (or as a variable within Python that can be printed using suitable commands).
I want this so that users of this program may learn better by understanding the underlying process that is going on real time, at the higher level (programming language execution).
I thought this would be possible especially because Python is an interpreter language, so the code is playing part until the penultimate step of executing it.
Is there any way to do this intrinsically? If not, I think there should be a way to write a program that will​ take another program as input and execute while also having access to source code. With some advanced parsing, that kind of design will be able to achieve this, but I'm looking for preferably a more natural way to do this.
This may not be perfect to teach using but surely exec would work?
As in:
mycommand = "a = 5**3"
print(mycommand)
exec(mycommand)
print("a = "+str(a))
I've been searching everywhere for an answer to this but to no avail. I want to be able to run my code and have the variables stored in memory so that I can perhaps set a "checkpoint" which I can run from in the future. The reason is that I have a fairly expensive function that takes some time to compute (as well as user input) and it would be nice if I didn't have to wait for it to finish every time I run after I change something downstream.
I'm sure a feature like this exists in PyCharm but I have no idea what it's called and the documentation isn't very clear to me at my level of experience. It would save me a lot of time if someone could point me in the right direction.
Turns out this is (more or less) possible by using the PyCharm console. I guess I should have realized this earlier because it seems so simple now (though I've never used a console in my life so I guess I should learn).
Anyway, the console lets you run blocks of your code presuming the required variables, functions, libraries, etc... have been specified beforehand. You can actually highlight a block of your code in the PyCharm editor, right click and select "Run in console" to execute it.
This feature is not implement in Pycharm (see pycharm forum) but seems implemented in Spyder.
This Python program enters fdisk. I see the output. fdisk is an interactive program. How do I get the Python program to pass an "m" to the first field and press enter?
import subprocess
a = "dev/sda"
x = subprocess.call(["fdisk", a])
print x
I'd rather not import a new module/library, but I could. I've tried different syntax with subprocess.call() and extra parameters in the above. Nothing seems to work. I get different errors. I've reviewed Python documentation. I want to feed input and press Enter in the subsequent, interactive menu options of fdisk.
Check out the pexpect library (I know you didn't want an extra module, but you want to use the best tool for the job). It's pure Python, with no compiled submodules, so installation is a snap. Basically, it does the same thing in Python as the classic Unix utility expect - spawns child applications, controls them, and responds to expected patterns in their output. It's great for automation, and especially application testing, where you can quickly feed the newest build of a command-line program a series of inputs and guide the interaction based on what output appears.
In case you just don't want another module at all, you can always fall back on the subprocess module's Popen() constructor. It spawns and creates a connection to a child process, allowing you to communicate with it as needed, and in fact pexpect relies a great deal on it. I personally think using pexpect is more intuitive than subprocess.Popen(), but that's just me. YMMV.
I like the python-send-buffer command, however I very often use Python embedded in applications, or launch Python via a custom package management system (to launch Python with certain dependencies).. In other words, I can't just run "python" and get a useful Python instance (something that python-send-buffer relies on)
What I would like to achieve is:
in any Python interpreter (or application that allows you to evaluate Python code), import a magic_emacs_python_server.py module (appending to sys.path as necessary)
In emacs, run magic-emacs-python-send-buffer
This would evaluate the buffer in the remote Python instance.
Seems like it should be pretty simple - the Python module listens on a socket, in a thread. It evaluates in the main thread, and returns the repr() of the result (or maybe captures the stdout/stderr, or maybe both). The emacs module would just send text to the socket, waits for a string in response, and displays it in a buffer.
Sounds so simple something like this must exist already... IPython has ipy_vimserver, but this is the wrong way around. There is also swank, while it seems very Lisp-specific, there is a Javascript backend which looks very like what I want... but searching finds almost nothing, other than some vague (possibly true) claims that SLIME doesn't work nicely with non-Lisp languages
In short:
Does a project exist to send code from an emacs buffer to an existing Python process?
If not, how would you recommend I write such a thing (not being very familiar with elisp) - SWANK? IPython's server code? Simple TCP server from scratch?
comint provides most of the infrastructure for stuff like this. There's a bunch of good examples, like this or this
It allows you to run a command, provides things comint-send-string to easily implement send-region type commands.
dbr/remoterepl on Github is a crude proof-of-concept of what I described in the question.
It lacks any kind of polish, but it mostly works - you import the replify.py module in the target interpreter, then evaluate the emacs-remote-repl.el after fixing the stupid hardcoded path to client.py
Doesn't shell-command give you what you are looking for? You could write a wrapper script or adjust the #! and sys.path appropriately.