Develop Reference

Why does the "which" system command give a 256 code with os.system in python?

I am on mac OSX.
I have a program where I am trying to call downloaded libraries from the terminal. This is not possible if I don't know where the libraries are. I will use pip as a common library example
>>> os.system("pip -h")
32512
>>> os.system("which pip")
256
I have read this response to the 256 error, however, I still don't understand why it appears here. It says it is "frequently used to indicate an argument parsing failure" however the exact command works because this does not seem to be an argument parsing error to me.
I would like to be able to do something to the effect of:
os.system(os.system("which pip") +" -h")
If there is another way of doing this, I would love to hear it

Don't use os.system like that (and don't use which, either). Try this to find a program:
import os
for bin_dir in os.environ.get("PATH").split(":"):
if 'my_program' in os.listdir(bin_dir):
executable_path = os.path.join(bin_dir, 'my_program')
break
Note that this does assume that PATH was properly set by whatever process started the script. If you are running it from a shell, that shouldn't be an issue.
In general, using os.system to call common *NIX utilities and trying to parse the results is unidiomatic-- it's writing python as if it was a shell script.
Then, instead of using system to run pip, use the solution describe in this answer.

How to save code at the python prompt in the terminal to a local file

I have just written a bunch of lines of code on the Python prompt at the terminal. Now, I want to save all those lines of code to a .py file.
I am unable to find out how to do that. The only thing that I could find on StackOverflow was this answer but it shows only how to do it in an iPython notebook. I am not using an iPython notebook. I am running the code at the command line on the terminal.
I tried to follow that answer (because just in case) and ran the %save magic command on the terminal but it gave a SyntaxError.
So, how do save it?
Thanks!

See http://blog.e-shell.org/174 . As wu explains, the python prompt is using readline, and you can import a Python library to access this.
>>> import readline
>>> readline.write_history_file('/path/to/history.txt')

You can trying using another interpreter : bpython , I belive it has what you need,check it out.
Save the code you've entered to a file.

You seem to be affected by the misconception, that the python environment is workspace-centered (similar to what I know from Smalltalk and some LISP variants):
fire up with an initial workspace
modify by your liking
store the result
This is unfortunately not the case. While you can import existing files, the other option is to specify an existing file as initially to be loaded and keep the interpreter open by using the -i option.

It really depends on your terminal for the exact commands.
The general idea is to copy everything (if possible) or one page at a time from the terminal into a text editor and then clean the >>> prompts (and possibly other formatting problems) in the text editor.
But anyway, typing a lot of commands directly in the execution environment if really bad practice. At least you test a handful of lines and immediately save them in a file. IDLE is great at this game...

How did I get informations on the module I'm writing?

I'm writing my first complete python project with Vim. As I was modifying a
file I accidentally hit several keys that I can't find back and I get this
prompt:
I didn't know it was possible to get this kind of help on a module I am
writing and I have no idea how I got it, so my question is:
What command or tools allows to generate this kind on module information?
Several notes
The command is not a Vim command because the ouput was in an external
shell (so I probably use an equivalent to :![command].
I don't have any Vim plugin related to python installed so it was probably not generated by a plugin.
The command wasn't issued in an interactive python prompt since I started my vim from my bash prompt.
I have not idea of how many keystrokes I used.
My Vim command history and my bash history doesn't have a trace of what
happened.
I'm using zsh and oh-my-zshell
I know that this question might sound silly but I have no idea of which tool can do that and I have no mean to find what sequence of keystrokes I used.

You can use pydoc command to get module help
pydoc requests
if you are using the interactive python shell, you can use the help function:
>>> import requests
>>> help(requests.get)
it work on class instance too

Python open default terminal, execute commands, keep open, AND then allow user-input

I'm wanting to open a terminal from a Python script (not one marked as executable, but actually doing python3 myscript.py to run it), have the terminal run commands, and then keep the terminal open and let the user type commands into it.
EDIT (as suggested): I am primarily needing this for Linux (I'm using Xubuntu, Ubuntu and stuff like that). It would be really nice to know Windows 7/8 and Mac methods, too, since I'd like a cross-platform solution in the long-run. Input for any system would be appreciated, however.
Just so people know some useful stuff pertaining to this, here's some code that may be difficult to come up with without some research. This doesn't allow user-input, but it does keep the window open. The code is specifically for Linux:
import subprocess, shlex;
myFilePathString="/home/asdf asdf/file.py";
params=shlex.split('x-terminal-emulator -e bash -c "python3 \''+myFilePathString+'\'; echo \'(Press any key to exit the terminal emulator.)\'; read -n 1 -s"');
subprocess.call(params);
To open it with the Python interpreter running afterward, which is about as good, if not better than what I'm looking for, try this:
import subprocess, shlex;
myFilePathString="/home/asdf asdf/file.py";
params=shlex.split('x-terminal-emulator -e bash -c "python3 -i \''+myFilePathString+'\'"');
subprocess.call(params);
I say these examples may take some time to come up with because passing parameters to bash, which is being opened within another command can be problematic without taking a few steps. Plus, you need to know to use to quotes in the right places, or else, for example, if there's a space in your file path, then you'll have problems and might not know why.
EDIT: For clarity (and part of the answer), I found out that there's a standard way to do this in Windows:
cmd /K [whatever your commands are]
So, if you don't know what I mean try that and see what happens. Here's the URL where I found the information: http://ss64.com/nt/cmd.html

Automating Subversion Commands using Python

I am pretty new to Subversion, and not that experienced in Python, but am doing some work with large volume of media-files that need moving around within the directory. Using the Visions GUI, some of the file transfers are taking a very long time, so I'd like to automate these tasks to run over night by storing the actions within a text file and then having a python script act on these overnight?
For example the text file might contain a command such as:
svn mv current desired
How can I send this string to Terminal to execute the command?

You could do os.system call or try using PySVN, which may give you more control in Python over SVN repository you're working with.

The subprocess module is the best way to execute commands. As #Abgan points out, the better way might be to use a subversion library instead.

If you're on Windows, it'd be better to use an SVN library. On Linux/Mac/Unix you could go either way realistically, because these can run a subprocess well - windows doesn't do terribly well at this.
subprocess is indeed preferred over os.system today.
The nice thing about using subprocess.Popen instead of an SVN library (module), is that you don't have to learn two ways of accessing SVN. Your command line SVN knowledge translates directly into your code.