Type `M-x cd` to change directory to the location of the program you wish to debug.
Type `M-x pdb`. You&#39;ll be prompted with `Run pdb (like this): pdb `. Enter the name of the program (e.g. `test.py`). 

At the `(Pdb)` prompt, type `help` to learn about how to use pdb.

Alternatively, you can put

    import pdb 
    pdb.set_trace()

right inside your program (e.g. `test.py`). Now type `M-x shell` to get a shell prompt. When you run your program, you&#39;ll be dumped into `pdb` at the point where `pdb.set_trace()` is executed.

For me, I needed to replace the default &quot;pdb&quot; with 

    python -m pdb myscript.py

The [`realgud`](https://github.com/realgud/realgud/) package (available from MELPA) supports PDB (among a gazillion other debuggers), and has a host of neat features that Emac&#39;s PDB doesn&#39;t have.

The one I like best is the shortkeys mode. Once you start debugging a program, you can press `n`, `s`, `c` etc. right in the source window, instead of having to type these commands in the PDB buffer. It also supports Visual-Studio style keybindings with function keys (`f10`, `f11`, `f5`, etc).

After installing RealGUD, you need to run `M-x load-feature realgud` to load it, and you can start `pdb` with `M-x realgud:pdb`.

In HTML (and in typography in general, I suppose), there appears to be some defined sizes for H1-H6 -elements.

Ie., if the baseline font size is 16px (or 100%), then h1 (w/c)ould be 2.25em (36px).
And H2 (w/c)ould be 1.5em (24px). Et cetera.
Where do these variables come from? The H1=36px, H2=24px, H3=21px, H4=18px, H5=16px, H6=14px, that is. (or, if you like, H1=2em, H2=1.5em, H3=1.17em, etc., the point isn&#39;t the numbers themselves, but the relation between them)

Is there some mathematical formula for them? Does it have something to do with golden ratio or fibonacci? I haven&#39;t been able to find information on this.

EDIT: to be more specific, what is the pattern; why does it go from 36 to 24 to 21, or start from 36 to begin with (or, if you like, from 2em to 1.5em to 1.17em, etc.)?

Oh, I forgot to specify where I came up with the original numbers, they&#39;re from [here](http://webtypography.net/Harmony_and_Counterpoint/Size/3.1.1/)

H1-H6 font sizes in HTML

I have a UITableView where when I put it in editing mode, I want selective rows to be selectable, however, they are not. Is there a way I can force them to be selectable?

Selecting row while UITableView is in editing mode

How to debug python programs in emacs? 

I use `python-mode.el`

I get reference like 
   

    import pdb; pdb.set_trace();

but not sure how to use it.


Debugging python programs in emacs

How to debug python programs in emacs?
I use <code>python-mode.el</code>
I get reference like
<pre><code class="hljs language-arduino">import pdb; pdb.set_trace();
</code></pre>
but not sure how to use it.

What is the correct way to fix this ImportError error?

I have the following directory structure:

    /home/bodacydo
    /home/bodacydo/work
    /home/bodacydo/work/project
    /home/bodacydo/work/project/programs
    /home/bodacydo/work/project/foo


And I am in the directory

    /home/bodacydo/work/project

Now if I type

    python ./programs/my_python_program.py

I instantly get

    ImportError: No module named foo.tasks

The `./programs/my_python_program.py` contains the following line:

    from foo.tasks import my_function

I can&#39;t understand why python won&#39;t find `./foo/tasks.py` - it&#39;s there.

If I do it from the Python shell, then it works:

    python
    &gt;&gt;&gt; from foo.tasks import my_function

It only doesn&#39;t work if I call it via `python ./programs/my_python_program.py` script.

How to fix &quot;ImportError: No module named ...&quot; error in Python?

I want to use Fabric to deploy my web app code to development, staging and production servers. My fabfile:

    def deploy_2_dev():
      deploy(&#39;dev&#39;)

    def deploy_2_staging():
      deploy(&#39;staging&#39;)

    def deploy_2_prod():
      deploy(&#39;prod&#39;)

    def deploy(server):
      print &#39;env.hosts:&#39;, env.hosts
      env.hosts = [server]
      print &#39;env.hosts:&#39;, env.hosts

Sample output:

    host:folder user$ fab deploy_2_dev
    env.hosts: []
    env.hosts: [&#39;dev&#39;]
    No hosts found. Please specify (single) host string for connection:

When I create a `set_hosts()` task as shown in the [Fabric docs][1], env.hosts is set properly. However, this is not a viable option, neither is a decorator. Passing hosts on the command line would ultimately result in some kind of shell script that calls the fabfile, I would prefer having one single tool do the job properly.

It says in the Fabric docs that &#39;env.hosts is simply a Python list object&#39;. From my observations, this is simply not true.

Can anyone explain what is going on here ? How can I set the host to deploy to ?


  [1]: http://docs.fabfile.org/0.9.0/usage/execution.html#globally-via-env

How to set target hosts in Fabric file

I need to launch a number of long-running processes with `subprocess.Popen`, and would like to have the `stdout` and `stderr` from each automatically piped to separate log files. Each process will run simultaneously for several minutes, and I want two log files (`stdout` and `stderr`) **per process** to be written to as the processes run.

Do I need to continually call `p.communicate()` on each process in a loop in order to update each log file, or is there some way to invoke the original `Popen` command so that `stdout` and `stderr` are automatically streamed to open file handles?

Piping output of subprocess.Popen to files

    datetime.datetime.utcnow()

Why does this `datetime` not have any timezone info given that it is explicitly a UTC `datetime`?

I would expect that this would contain `tzinfo`.

Why does datetime.datetime.utcnow() not contain timezone information?

I am using Python to write chunks of text to files in a single operation:

    open(file, &#39;w&#39;).write(text)

If the script is interrupted so a file write does not complete I want to have no file rather than a partially complete file. Can this be done?


How to make file creation an atomic operation?

Regular expressions can become quite complex.  The lack of white space makes them difficult to read.  I can&#39;t step though a regular expression with a debugger.  So how do experts debug complex regular expressions?

How do you debug a regex?

What are best ways to Debug Clojure code, while using the repl?

Debugging in Clojure?

I was using the Java debugger within IntelliJ 8 and noticed a button labeled &quot;drop frame&quot;. Does anybody know what purpose this serves?  How/why would this be used/useful?


When using the Java debugger in IntelliJ, what does &quot;Drop Frame&quot; mean?

Why do so many [`assertEquals()`][1] or similar function take the expected value as first parameter and the actual one as second ?  
This seems counter-intuitive to me, so is there a particular reason for this unusual order ?


  [1]: https://docs.python.org/3/library/unittest.html#unittest.TestCase.assertEqual

Why are assertEquals() parameters in the order (expected, actual)?

I have some variables inside a template and I don&#39;t know where I assigned them. I need to know what is inside a particular variable; for instance, say I have a variable in smarty called `member`. I tried with `{debug}` but it didn&#39;t work, and no popup was shown. 

How can I output/debug smarty variables using something like `var_dump()` inside the templates?

How to Debug Variables in Smarty like in PHP var_dump()

I would like rainbow parens for editing Clojure in Emacs and since [VI does this][1] I assume that in Emacs it should be something like M-x butterfly or something :)


  [1]: http://www.vim.org/scripts/script.php?script_id=1230

How do I get &quot;rainbow parentheses&quot; in emacs?

What is the easiest way to move selected region or line (if there is no selection) up or down in emacs? I&#39;m looking for the same functionality as is in eclipse (bounded to M-up, M-down).

Move line/region up and down in emacs

`ess-mode` is &quot;Emacs speaks statistics.&quot; This mode is useful for editing programs for R or Splus (two separate statistics packages).

In my buffer, when ever I type `_` the character is replaced with `&lt;-`, which is very frustrating.  Is there an emacs lisp statement to turn off this behavior?

emacs: 22.1.1
ess-mode release (unknown)

How to stop emacs from replacing underbar with &lt;- in ess-mode

I have setup my windows in a certain way.  How do I save this setting to be invoked later?

Preserve window layout in Emacs

Quick question: How do I specify the number of characters in a split window?  C-x-3 Splits my window into two windows evenly, but a subsequent split will split one of the windows in half. I&#39;d like 3 equal sized windows.  The documentation says that I should be able to specify the number of characters for the left buffer as a parameter, but I cant seem to get that to work.  Any ideas for syntax? 

Thanks.

emacs split into 3 even windows

I am using py.test for unit testing my python program. I wish to debug my test code with the python debugger the normal way (by which I mean pdb.set_trace() in the code) but I can&#39;t make it work. 

Putting pdb.set_trace() in the code doesn&#39;t work (raises IOError: reading from stdin while output is captured). I have also tried running py.test with the option --pdb but that doesn&#39;t seem to do the trick if I want to explore what happens before my assertion. It breaks when an assertion fails, and moving on from that line means terminating the program.

Does anyone know a way to get debugging, or is debugging and py.test just not meant to be together?


Can I debug with python debugger when using py.test somehow?

I want to add [pdb]—the Python debugger—to my toolbox. What&#39;s the best way to get started?

[pdb]: http://docs.python.org/2/library/pdb.html


Getting started with the Python debugger, pdb

Is there a way to automatically start the debugger at the point at which a unittest fails?

Right now I am just using pdb.set_trace() manually, but this is very tedious as I need to add it each time and take it out at the end.

For Example:

    import unittest

    class tests(unittest.TestCase):

        def setUp(self):
            pass

        def test_trigger_pdb(self):
            #this is the way I do it now
            try:
                assert 1==0
            except AssertionError:
                import pdb
                pdb.set_trace()

        def test_no_trigger(self):
            #this is the way I would like to do it:
            a=1
            b=2
            assert a==b
            #magically, pdb would start here
            #so that I could inspect the values of a and b

    if __name__==&#39;__main__&#39;:
        #In the documentation the unittest.TestCase has a debug() method
        #but I don&#39;t understand how to use it
        #A=tests()
        #A.debug(A)

        unittest.main()



Python Unit Testing: Automatically Running the Debugger when a test fails

`nosetests --pdb` let&#39;s me halt upon error or failure, but this is too late for my needs. Stepping through code during execution helps me debug where the problem is.

However, nosetests are helpful as they allow tests that rely on relative imports (i.e. tests in a package).

How can I set breakpoints before the tests are executed?
Currently I&#39;m using:

    python -m pdb /path/to/my/nosetests testfile.py

This solution isn&#39;t adequate. Nosetests interfere with pdb output, and my keyboard controls (e.g. arrow keys) are broken.

Using import pdb; pdb.set_trace() would seem like a good idea, however nosetests is blocking my access to the pdb console. 

setting breakpoints with nosetests --pdb option

In the perl debugger, if you repeatedly list segments of code taking you away from the current line, you can return to the current line by entering the command `.` (dot).   

I have not been able to find anything comparable using the python PDB module.  If I _list_ myself away from the current line and want to view it again, it seems I have to either remember the line number that was currently executing (unlikely for me) or execute a statement (often undesirable).  

Am I missing something?



Content Type	Original Author	Original Content on Stackoverflow
Question	user90150	View Question on Stackoverflow
Solution 1 - Python	unutbu	View Answer on Stackoverflow
Solution 2 - Python	Ben	View Answer on Stackoverflow
Solution 3 - Python	Clément	View Answer on Stackoverflow

Debugging python programs in emacs

Python Problem Overview

Python Solutions

Solution 1 - Python

Solution 2 - Python

Solution 3 - Python

Selecting row while UITableView is in editing mode

H1-H6 font sizes in HTML

Attributions