Develop Reference

Hard times with IDLE

So I've been working with Python on my computer for about the last 2 months with no issues. Just recently however, something went wrong with IDLE. I am running python 2.5
I used to be able to right-click and select "Edit with IDLE" for a python program. That option no longer is available. When I try "open with" and navigate to the idlelib in python, I can select idle.bat, idle.py, or idle.py (no console). I've tried each option and each fails to open and returns an error that either it is not a valid Win32 application or that "Windows cannot find idle.pyw"
I am able to open IDLE on its own and use the open function in IDLE to open files, but can't open files directly using IDLE as I could before.
There was formerly the White background icon with the python logo, which is now replace by windows' logo for no program (white square, blue and red dots). I have tried to repair-install and unistall-re-install both with no success. There is no firewall or antivirus, and it was installed with permissions for all users.
Any help is much appreciated, this has been maddeningly difficult to figure out.

The native one that comes with python on windows is problematic at times, so you could uninstall and reinstall it as a solution, or open it from its directory instead of a shortcut, or get another IDE. I recommend the Ninja IDE very nice and light looking, or if you're on linux you could just use vim from terminal.
Also, if it's extremely necessary, try upgrading your python version and IDE. I think the IDE included for windows looks like a modified emacs to be honest.

The fact that Windows changed the right-context menu for .py files has nothing to do with Idle, and probably nothing to do with Python either. You are not the first to have this problem. You can potentially restore 'Edit with Idle' but without directly editing the registry (an expert option) I only knew how to do so in XP. You might also be able to fix it be going back to a restore point before it changed, but you would lose all updates since, so I would not do that.
I am surprised that re-installing did not restore it. The line was once gone for me, too, and was restored by a recent install.
I have Win7. I just now tried 'Open with', navigated to 3.4 idlelib, and selected idle.bat (the .py files were not offered as a choice). The .py file opened in an Idle editor just fine. It is now a permanent option for Open with, without having to navigate.
Idle has gotten perhaps 150 patches since 2.5. Even if you have to edit programs to run on 2.5, I strongly recommend installing a current version of Python and Idle.
I have no ideal what your comment "the programs still can't find anything associated with it, like Tkinter for example " means.

python 3 in emacs

I changed two days ago to Emacs 23, which lately gave me a lot of headache, especially, as I have two Python versions installed, the older 2.7 and 3. As I generally want to start the python 3 interpreter, it would be nice if I could tell Emacs in some way to use python 3 instead of 2.7.
Besides, I could not find a module which helps to highlight python3 syntax. I am currently using python-mode.el for highlighting.
Also, if somebody had a good tip for which module would be best to show the pydoc, I would be very thankful.
Thanks in advance!

If you're using python-mode.el, you can specify the binary to be executed as an inferior process by setting the py-python-command variable, i.e.:
(setq py-python-command "python3")
Naturally, you'll need to provide the name of the binary as it exists on your system in place of "python3", if it differs. In python.el, the analogous variable to set is python-python-command.
As far as using pydoc, there are a few possibilities. First, you can simply execute help() inside the Python inferior process. If you do choose that option, you might find it useful to add the following code to your .emacs file:
(setenv "PAGER" "cat")
This is necessary because interactive pagers (e.g., less, more, most, etc.) don't work particularly well inside inferior process buffers. Second, you can install a Texinfo package containing the documentation and use Emacs's info browser (q.v., Python Programming in Emacs). Finally, if you opt to use python.el, it includes an interactive function called python-describe-symbol that can lookup pydoc help on demand (and I suspect python-mode.el should have something similar). If you search around a bit, I'm sure you can find other methods and/or third-party packages as well.

[RET] = enter or return key.
M = Meta or Alt key.
If you feel like letting Emacs do the heavy lifting for you, go through the Emacs settings dialogue to have Emacs set it automatically.
M-x customize-variable [RET] python-shell-interpreter [RET]
A new buffer should appear where you can customize the python interpreter you are using.
The field to the right of Python Shell Interpreter: will be the current interpreter your are using. In my case it was python so I changed it to python3. Then move the curer to select the Apply and Save button above and hit [RET] to make Emacs respect the new setting. Alternatively you can click the button with the mouse.
Next time you open the Emacs python interpreter, it will be using the new python you set from the setting dialogue.

After I did the following thing, I got the behavior that: when editing a Python file in emacs, C-c C-p creates a new buffer with a Python3 interpreter.
Add to your .emacs file the following:
(defcustom python-shell-interpreter "python3"
"Default Python interpreter for shell."
:type 'string
:group 'python)
The reason I tried this, was because I found
(defcustom python-shell-interpreter "python"
"Default Python interpreter for shell."
:type 'string
:group 'python)
in python.el. And I hypothesized (i) that the "python" could be substituted with "python3" and (ii) that this would override the definition in python.el.
It is likely that there are reasons why this is inelegant or heavy-handed or otherwise bad. I am an emacs newb.

start an python-interpreter
M-x python RET
(the default interpreter)
M-x pythonVERSION
where VERSION means any installed version

Inspired by #serv-inc's answer you can also put
(setq python-shell-interpreter "python3")
into your ./.emacs.d/init.el or where you store your configuration.

It's December 2020, I'm using EMACS 25, otherwise unconfigured for python, and I found that:
(setq python-shell-interpreter "python3")
added to my .emacs file did the business and led to a reasonably intuitive way of working with python3. C-c C-c sends my file to the interpreter (or asks me to start a new interpreter, and tells me how).
Of course, now the python3 interpreter runs for any python file, so python 2 programs don't work.
I am imagining a better world where emacs looks at the #!/usr/bin/env python2 line at the top of my file and figures out which interpreter to start by some kind of insane high-tech magic.

Note python-mode.el knows a hierarchy how to detect the version needed
a shebang precedes setting of py-shell-name
while py-execute-THING-PYTHONVERSION
would precede also shebang for the command being
see menu PyExec

How do I run a python interpreter in Emacs?

I just downloaded GNU emacs23.4, and I already have python3.2 installed in Windows7.
I have been using Python IDLE to edit python files.
The problem is that I can edit python files with Emacs but I do not know how to run python interpreter in Emacs. When i click on "switch to interpreter", then it says "Searching for program: no such file or directory, python"
Someone says i need to make some change on .emacs file, but i do not know where to look for.
And I am very unexperienced and just started to learn programming. I am not familiar with commonly used terminologies. I have been searching for solutions but most of the articles i find on the Internet only confuse me.
so the questions are:
how do i run python interpreter in Emacs?
are there different kind of python interpreter? if so, why do they have different interpreters for one language?

Place this in your .emacs file to set the location of your python interpreter:
(setq python-shell-interpreter "path\to\your\python3.2")
Emacs comes with good manuals and an info mode to help read them. To learn more about .emacs you can use:
M-: (info "(Emacs)Init file") RET.

C-c C-z can do this. It is the key-binding for the command python-switch-to-python

In emacs 25.3.1 I use this to open up a python shell:
M-x run-python
After first adding this to my .emacs file:
(setq python-shell-interpreter "/usr/local/bin/python3")

IF you have python installed, try M-x python-shell
(press and hold ALT while pressing x, then type python-shell, then press enter)
There are different language implementations if that is what you are asking (see a list of them here).

In emacs 24.5.1 with spacemacs 105 (develop branch) and the Python layer enabled ("layer" is a spacemacs concept; see their documentation), I find python-shell-switch-to-shell opens an IPython buffer. I tested macropy.console in such a buffer and it works great.

You probably need to have Python in your windows PATH environment variable. Can you start the interpreter just by typing python in the command window?
I don't have anything special in my emacs.el, but the start interpreter command works just fine.
Also, I recommend reading this blog post, as it contains many useful tips and packages worth installing if using Emacs as a Python IDE.

To simply open an interpreter, you can also use M-x python. If that does not work, try M-x python and hit TAB, which will list more options via auto-completion. One of them should work k if you have python installed.
If you are inclined, it may be worthwhile to check out the Emacs python modes as well - http://www.emacswiki.org/emacs/?action=browse;oldid=PythonMode;id=PythonProgrammingInEmacs

In emacs 24.2 there is python-switch-to-python

Emacs Python-mode syntax highlighting

I have GNU Emacs 23 (package emacs23) installed on an Ubuntu 10.04 desktop machine and package emacs23-nox installed on an Ubuntu 10.04 headless server (no X installed). Both installations have the same ~/.emacs file. I run Emacs with -nw on both computers. I don't have python-mode installed on either machine as my understanding is that this is included in Emacs 23.
On the desktop machine, comments in Python (starting with #) are highlighted in red. On the server, comments appear in plain white text like all other non-highlighted text. Any suggestions as to why comments are not being highlighted correctly on the server (nox) installation?
Update: This appears to be a terminal-related issue. I ssh into the server machine from terminator via the screen replacement byobu. If I run emacs on the server with TERM="xterm-256color" emacs, then comments are highlighted, but all the other colours look very strange.
Update: Adding `export TERM="xterm-256color" "solved" this. The syntax highlighting now has very strange colours though: purples lilacs and light browns. My green current line highlight bar is now a light pale yellow/green. Comments are highlighted in red though :)
Update: Solved. Setting TERM="xterm-color" produces "proper" colors, including highlighting of comments. The server was defaulting to a value of "screen-bce" for TERM which was not highlighting comments.
Update: Unsolved. byobu provides keybindings for various function keys to easily create new screen sessions and switch between them. When TERM is set to xterm-color, these function keys no longer work. So I guess I'll just have to be happy with unhighlighted comments in Python code in Emacs.

For me running emacs -nw from inside byobu with TERM=xterm produced the correct colours for syntax highlighting (the comments in python and bash are all red not just the #) and the function keys work. Note I set TERM as part of an alias for running emacs rather than setting it generally in .bashrc:
alias emacs='TERM=xterm; emacs -nw'
See also this post: Terminal emacs colors only work with TERM=xterm-256color

I don't have the programs you are using installed to test this, but I did notice some differences in the way the function keys are defined between screen-bce and xterm-color. You can try using the below steps to copy the settings from screen-bce to xterm-color.
Using the infocmp program, you can view the differences between the terminfo settings for two TERM settings:
infocmp -d screen-bce xterm-color
You can use infocmp to decompile the terminfo file to its source and make changes to it to try to mimic the behavior of the other terminal. Start by decoding the xterm-color terminfo file.
infocmp xterm-color > xterm-color.src
Edit xterm-color.src and modify the definitions of the kf1 through kf19 fields to match the values for screen-bce. Use infocmp to see screen-bce's definitions.
infocmp screen-bce
Finally compile using the tic program.
tic xterm-color.src
If you run it as a non-root user, it will put the compiled terminfo file into $HOME/.terminfo directory. On my system, it seems like Ubuntu picks this up automatically. You can also install it into the standard /usr/share/terminfo when you're satisfied. Running tic as root should do this for you.
Good luck!

I just added
(set-face-foreground 'font-lock-comment-face "red")
to my .emacs

How to fix pdb in Aquamacs on Mac OS X?

I'm developing a django app using aquamacs as my ide. Pdb isn't working since upgrading to emacs 23.2.1 using python 2.6.1. When I invoke pdb like this:
M-x pdb
Run pdb (like this): pdb ./manage.py runserver
The gud-manage.py frame appears with this message (and nothing more) -
Current directory is /path/to/my/source/
It isn't responsive to keyboard input, though I can right-click and send a quit or kill signal. It seems like emacs isn't capturing the pdb output correctly.
Has anyone seen this and (hopefully) fixed it? I believe it has something to do with the gud-pdb-marker-regexp variable (see point #2 in link).
Related issues
Seems to have been around since 2007
One person a solution for this problem on Windows (adding -u to the python command in the pdb script). I tried it anyway, but this didn't work for me.

Same issue (Current directory is ...) to me with emacs 23.2 (9). As you mentioned, it is caused by a CR/LF ending and can be fixed by setting the gud-pdb-marker-regexp.
I added the CR (\r) to the gud-pdb-marker-regexp. May you want to add the following line to your .emacs file and give it a try.
(setq gud-pdb-marker-regexp "^> \\([-axx-zA-Z0-9_/.:\\]*\\|<string>\\)(\\([0-9]+\\))\\([a-zA-Z0-9_]*\\|\\?\\|<module>\\)()\\(->[^\n\r]*\\)?[\n\r]")

Not sure if that is the case for you, but just to mention it: PDB hangs for me in Emacs when the source code path contains a space - when I move the python file to a directory without a space in the name, it works (on Emacs 23.1.1).

I have been having this same issue. I had it fixed in 23.1 (http://debbugs.gnu.org/db/56/5653.html) but now in 23.2 that fix no longer works, or at least it doesn't appear to for me. I've just submitted a bug to Emacs explaining the problem in detail and hopefully it will get resolved.
A workaround for this is to execute pdb from the emacs shell:
Open the shell: M-x shell
Enter this in the shell: pdb
This will get pdb working properly within the shell.