I'd like to get help(obj) text in IPython or Jupyter notebook in a non-interactive manner, into some variable instead of it being displayed.
Note: help provides more information than obj.__doc__ provides, so that's not quite an alternative.
Short answer:
import pydoc
help_result_string = pydoc.render_doc(obj)
Longer answer:
When you call help(obj), it is a wrapper to pydoc.help(obj) (see help.__doc__), which is the same as pydoc.Helper()(obj) (from pydoc source: help = Helper()), which usually leads to pydoc.doc(obj), which writes the resulting string from pydoc.render_doc(obj) to the standard output or a pager, depending on the system.
Details on what other things can happen when help(obj) is called can be found in the pydoc source code.
These days, I'm transitiong from Matlab to Python after using Matlab/Octave for more than ten years. I have two quick questions:
In the Python interactive mode, is there anything corresponding to Matlab's ans?
How can I run shell commands in the Python interactive mode? Of course, I can use os.system(), but in Matlab we may run shell commands just by placing ! before the actual command. Is there anything similar in Python?
Python interactive mode is Python. You will need to use os.system or an equivalent. Alternately, you can suspend Python with Ctrl-Z, and get back into it with fg. (Assuming UNIX-like environment.)
The last evaluated expression is saved in the variable _:
>>> 1 + 2
3
>>> _ * 4
12
The Python equivalent of the Matlab ans is as follows:
ans = (your_expression)
In other words, the most recent expression is not always automatically saved to a default reference, so just save it manually as normal. As #Amadan points out, expressions are sometimes saved to _, but not always. The best practice for reliability and clarity is to save it yourself.
To run shell commands, you can use os.system() as you suggested. However, that is deprecated, so you should look into the subprocess module.
You probably want to use the IPython shell (now part of the jupyeter project). In the IPython shell you can also run system commands using !, although many basic commands (like ls or cd) work without even needing to !. Unlike in MATLAB, you don't need to pass it as a string (although you can). So !ls works fine in IPython, while in MATLAB you would need to do !'ls'. Further, you can assign the results to a variable in IPython, which you can't do in MATLAB. So a = !ls works in IPython but not in MATLAB. Further, if you use !!, the result is returned in a form easily usable in Python. So !!ls returns a list of file names.
IPython still uses the _ notation for getting the previous result (except, as with Python, None is counted as "no result" and thus is not recorded). You can also get the second-to-last result with __ and the third-to-last with ___. Further, IPython puts a number next to each line in the command prompt. To get the result of a particular line, just do _n where n is the number. So to get the result of the 3rd command, which has the number 3 next to it, just do _3. This still doesn't work if the result is None, though.
It has a ton of features. You can get the previous input (as a string) with _i (and so on, following the same pattern as with the outputs). You can time code with %timeit and %%timeit. You can jump into the debugger after encountering an error.
I would like to print into the terminal window that runs IPython Notebook and not into the cell output. Printing into cell output consumes more memory and slows down my system when I issue a substantial number of print calls. In essence, I would like this behaviour by design.
I have tried the following:
I tried a different permutations of print and sys.stdout.write calls
I looked at the IPython Notebook documentation here, here and here without help
I have tried using this as a workaround but it seems to be only working on Python 2.7
You have to redirect your output to the systems standard output device. This depends on your OS. On Mac that would be:
import sys
sys.stdout = open('/dev/stdout', 'w')
Type the above code in an IPython cell and evaluate it. Afterwards all output will show up in terminal.
On Windows, this can work:
import sys
sys.stdout = open(1, 'w')
In order to be able to switch form one to the other easily:
terminal_output = open('/dev/stdout', 'w')
print('this will show up in the IPython cell output')
print('this will show up in the terminal', file=terminal_output)
Similarly, terminal_error = open('/dev/stderr', 'w') can be used to send to the terminal stderr, without any conflict with the default behavior of sys.stderr (which is to print an error message in the IPython cell output).
Via
import win32com.client
wordapp = win32com.client.gencache.EnsureDispatch('Word.Application')
I can get a Word Application object documented e.g. here. However, ipython's autocompletion is not aware of that API, is there any way to add that?
Quick solution
Perhaps the simplest way to achieve code completion in IPython (tested with 6.2.1, see the answer below for a snippet that works with 7.1) and Jupyter is to run the following snippet:
from IPython.utils.generics import complete_object
import win32com.client
#complete_object.when_type(win32com.client.DispatchBaseClass)
def complete_dispatch_base_class(obj, prev_completions):
try:
ole_props = set(obj._prop_map_get_).union(set(obj._prop_map_put_))
return list(ole_props) + prev_completions
except AttributeError:
pass
Short story long
With some more details being outlined in this guide, win32com ships with a script, makepy.py for generating Python types corresponding to the type library of a given COM object.
In the case of Word 2016, we would proceed as follows:
C:\Users\username\AppData\Local\Continuum\Anaconda3\pkgs\pywin32-221-py36h9c10281_0\Lib\site-packages\win32com\client>python makepy.py -i "Microsoft Word 16.0 Object Library"
Microsoft Word 16.0 Object Library
{00020905-0000-0000-C000-000000000046}, lcid=0, major=8, minor=7
>>> # Use these commands in Python code to auto generate .py support
>>> from win32com.client import gencache
>>> gencache.EnsureModule('{00020905-0000-0000-C000-000000000046}', 0, 8, 7)
The location of makepy.py will of course depend on your Python distribution. The script combrowse.py, available in the same directory, can be used to find the names of available type libraries.
With that in place, win32com.client will automatically make use of the generated types, rather than the raw IPyDispatch, and at this point, auto-completion is available in e.g. IPython or Jupyter, given that the COM object of interest actually publishes its available properties and methods (which is not a requirement).
Now, in your case, by invoking EnsureDispatch instead of Dispatch, the makepy part of the process is performed automatically, so you really should be able to obtain code completion in IPython for the published methods:
Note, though, that while this does give code completion for methods, the same will not be true for properties. It is possible to inspect those using the _prop_map_get_ attribute. For example, wordapp.Selection.Range.Font._prop_map_get_ gives all properties available on fonts.
If using IPython is not a strong requirement, note also that the PythonWin shell (located around \pkgs\pywin32\Lib\site-packages\pythonwin\Pythonwin.exe) has built-in code completion support for both properties and methods.
This, by itself, suggests that the same is achievable in IPython.
Concretely, the logic for auto-completion, which in turn relies on _prop_map_get_, can be found in scintilla.view.CScintillaView._AutoComplete. On the other hand, code completion in IPython 6.2.1 is handled by core.completer.IPCompleter. The API for adding custom code completers is provided by IPython.utils.generics.complete_object, as illustrated in the first solution above. One gotcha is that with complete_object being based on simplegeneric, only one completer may be provided for any given type. Luckily, all types generated by makepy will inherit from win32com.client.DispatchBaseClass.
If this turns out to ever be an issue, one can also circumvent complete_object entirely and simply manually patch IPython by adding the following five lines to core.completer.Completion.attr_matches:
try:
ole_props = set(obj._prop_map_get_).union(set(obj._prop_map_put_))
words += list(ole_props)
except AttributeError:
pass
Conversely, IPython bases its code-completion on __dir__, so one could also patch gencache, which is where the code generation ultimately happens, to include something to like
def __dir__(self):
return list(set(self._prop_map_get_).union(set(self._prop_map_put_)))
to each generated DispatchBaseClass.
fuglede's answer is great, just want to update it for the newest versions of IPython (7.1+).
Since IPython.utils.generics has changes from using simplegeneric to using functools, the #complete_object.when_type method should be changed to #complete_object.register. So his initial code should changed to:
from IPython.utils.generics import complete_object
import win32com.client
#complete_object.register(win32com.client.DispatchBaseClass)
def complete_dispatch_base_class(obj, prev_completions):
try:
ole_props = set(obj._prop_map_get_).union(set(obj._prop_map_put_))
return list(ole_props) + prev_completions
except AttributeError:
pass
From what I have read, there are two ways to debug code in Python:
With a traditional debugger such as pdb or ipdb. This supports commands such as c for continue, n for step-over, s for step-into etc.), but you don't have direct access to an IPython shell which can be extremely useful for object inspection.
Using IPython by embedding an IPython shell in your code. You can do from IPython import embed, and then use embed() in your code. When your program/script hits an embed() statement, you are dropped into an IPython shell. This allows the full inspection of objects and testing of Python code using all the IPython goodies. However, when using embed() you can't step-by-step through the code anymore with handy keyboard shortcuts.
Is there any way to combine the best of both worlds? I.e.
Be able to step-by-step through your code with handy pdb/ipdb keyboard shortcuts.
At any such step (e.g. on a given statement), have access to a full-fledged IPython shell.
IPython debugging as in MATLAB:
An example of this type of "enhanced debugging" can be found in MATLAB, where the user always has full access to the MATLAB engine/shell, and she can still step-by-step through her code, define conditional breakpoints, etc. From what I have discussed with other users, this is the debugging feature that people miss the most when moving from MATLAB to IPython.
IPython debugging in Emacs and other editors:
I don't want to make the question too specific, but I work mostly in Emacs, so I wonder if there is any way to bring this functionality into it. Ideally, Emacs (or the editor) would allow the programmer to set breakpoints anywhere on the code and communicate with the interpreter or debugger to have it stop in the location of your choice, and bring to a full IPython interpreter on that location.
What about ipdb.set_trace() ? In your code :
import ipdb; ipdb.set_trace()
update: now in Python 3.7, we can write breakpoint(). It works the same, but it also obeys to the PYTHONBREAKPOINT environment variable. This feature comes from this PEP.
This allows for full inspection of your code, and you have access to commands such as c (continue), n (execute next line), s (step into the method at point) and so on.
See the ipdb repo and a list of commands. IPython is now called (edit: part of) Jupyter.
ps: note that an ipdb command takes precedence over python code. So in order to write list(foo) you'd need print(list(foo)), or !list(foo) .
Also, if you like the ipython prompt (its emacs and vim modes, history, completions,…) it's easy to get the same for your project since it's based on the python prompt toolkit.
You can use IPython's %pdb magic. Just call %pdb in IPython and when an error occurs, you're automatically dropped to ipdb. While you don't have the stepping immediately, you're in ipdb afterwards.
This makes debugging individual functions easy, as you can just load a file with %load and then run a function. You could force an error with an assert at the right position.
%pdb is a line magic. Call it as %pdb on, %pdb 1, %pdb off or %pdb 0. If called without argument it works as a toggle.
(Update on May 28, 2016) Using RealGUD in Emacs
For anyone in Emacs, this thread shows how to accomplish everything described in the OP (and more) using
a new important debugger in Emacs called RealGUD which can operate with any debugger (including ipdb).
The Emacs package isend-mode.
The combination of these two packages is extremely powerful and allows one to recreate exactly the behavior described in the OP and do even more.
More info on the wiki article of RealGUD for ipdb.
Original answer:
After having tried many different methods for debugging Python, including everything mentioned in this thread, one of my preferred ways of debugging Python with IPython is with embedded shells.
Defining a custom embedded IPython shell:
Add the following on a script to your PYTHONPATH, so that the method ipsh() becomes available.
import inspect
# First import the embed function
from IPython.terminal.embed import InteractiveShellEmbed
from IPython.config.loader import Config
# Configure the prompt so that I know I am in a nested (embedded) shell
cfg = Config()
prompt_config = cfg.PromptManager
prompt_config.in_template = 'N.In <\\#>: '
prompt_config.in2_template = ' .\\D.: '
prompt_config.out_template = 'N.Out<\\#>: '
# Messages displayed when I drop into and exit the shell.
banner_msg = ("\n**Nested Interpreter:\n"
"Hit Ctrl-D to exit interpreter and continue program.\n"
"Note that if you use %kill_embedded, you can fully deactivate\n"
"This embedded instance so it will never turn on again")
exit_msg = '**Leaving Nested interpreter'
# Wrap it in a function that gives me more context:
def ipsh():
ipshell = InteractiveShellEmbed(config=cfg, banner1=banner_msg, exit_msg=exit_msg)
frame = inspect.currentframe().f_back
msg = 'Stopped at {0.f_code.co_filename} at line {0.f_lineno}'.format(frame)
# Go back one level!
# This is needed because the call to ipshell is inside the function ipsh()
ipshell(msg,stack_depth=2)
Then, whenever I want to debug something in my code, I place ipsh() right at the location where I need to do object inspection, etc. For example, say I want to debug my_function below
Using it:
def my_function(b):
a = b
ipsh() # <- This will embed a full-fledged IPython interpreter
a = 4
and then I invoke my_function(2) in one of the following ways:
Either by running a Python program that invokes this function from a Unix shell
Or by invoking it directly from IPython
Regardless of how I invoke it, the interpreter stops at the line that says ipsh(). Once you are done, you can do Ctrl-D and Python will resume execution (with any variable updates that you made). Note that, if you run the code from a regular IPython the IPython shell (case 2 above), the new IPython shell will be nested inside the one from which you invoked it, which is perfectly fine, but it's good to be aware of. Eitherway, once the interpreter stops on the location of ipsh, I can inspect the value of a (which be 2), see what functions and objects are defined, etc.
The problem:
The solution above can be used to have Python stop anywhere you want in your code, and then drop you into a fully-fledged IPython interpreter. Unfortunately it does not let you add or remove breakpoints once you invoke the script, which is highly frustrating. In my opinion, this is the only thing that is preventing IPython from becoming a great debugging tool for Python.
The best you can do for now:
A workaround is to place ipsh() a priori at the different locations where you want the Python interpreter to launch an IPython shell (i.e. a breakpoint). You can then "jump" between different pre-defined, hard-coded "breakpoints" with Ctrl-D, which would exit the current embedded IPython shell and stop again whenever the interpreter hits the next call to ipsh().
If you go this route, one way to exit "debugging mode" and ignore all subsequent breakpoints, is to use ipshell.dummy_mode = True which will make Python ignore any subsequent instantiations of the ipshell object that we created above.
You can start IPython session from pudb and go back to the debugging session as you like.
BTW, ipdb is using IPython behind the scenes and you can actually use IPython functionality such as TAB completion and magic commands (the one starts with %). If you are OK with ipdb you can start it from IPython using commands such as %run and %debug. ipdb session is actually better than plain IPython one in the sense you can go up and down in the stack trace etc. What is missing in ipdb for "object inspection"?
Also, python.el bundled with Emacs >= 24.3 has nice ipdb support.
Looks like the approach in #gaborous's answer is deprecated.
The new approach seems to be:
from IPython.core import debugger
debug = debugger.Pdb().set_trace
def buggy_method():
debug()
Prefixing an "!" symbol to commands you type in pdb seems to have the same effect as doing something in an IPython shell. This works for accessing help for a certain function, or even variable names. Maybe this will help you to some extent. For example,
ipdb> help(numpy.transpose)
*** No help on (numpy.transpose)
But !help(numpy.transpose) will give you the expected help page on numpy.transpose. Similarly for variable names, say you have a variable l, typing "l" in pdb lists the code, but !l prints the value of l.
You can start IPython from within ipdb.
Induce the ipdb debugger1:
import idpb; ipdb.set_trace()
Enter IPython from within in the ipdb> console2:
from IPython import embed; embed()
Return to the ipdb> console from within IPython:
exit
If you're lucky enough to be using Emacs, things can be made even more convenient.
This requires using M-x shell. Using yasnippet and bm, define the following snippet. This will replace the text ipdb in the editor with the set-trace line. After inserting the snippet, the line will be highlighted so that it is easily noticeable and navigable. Use M-x bm-next to navigate.
# -*- mode: snippet -*-
# name: ipdb
# key: ipdb
# expand-env: ((yas-after-exit-snippet-hook #'bm-toggle))
# --
import ipdb; ipdb.set_trace()
1 All on one line for easy deletion. Since imports only happen once, this form ensures ipdb will be imported when you need it with no extra overhead.
2 You can save yourself some typing by importing IPython within your .pdbrc file:
try:
from IPython import embed
except:
pass
This allows you to simply call embed() from within ipdb (of course, only when IPython is installed).
Did you try this tip?
Or better still, use ipython, and call:
from IPython.Debugger import Tracer; debug_here = Tracer()
then you can just use
debug_here()
whenever you want to set a breakpoint
the right, easy, cool, exact answer for the question is to use %run macro with -d flag.
In [4]: run -d myscript.py
NOTE: Enter 'c' at the ipdb> prompt to continue execution.
> /cygdrive/c/Users/mycodefolder/myscript.py(4)<module>()
2
3
----> 4 a=1
5 b=2
One option is to use an IDE like Spyder which should allow you to interact with your code while debugging (using an IPython console, in fact). In fact, Spyder is very MATLAB-like, which I presume was intentional. That includes variable inspectors, variable editing, built-in access to documentation, etc.
If you type exit() in embed() console the code continue and go to the next embed() line.
The Pyzo IDE has similar capabilities as the OP asked for. You don't have to start in debug mode. Similarly to MATLAB, the commands are executed in the shell. When you set up a break-point in some source code line, the IDE stops the execution there and you can debug and issue regular IPython commands as well.
It does seem however that step-into doesn't (yet?) work well (i.e. stopping in one line and then stepping into another function) unless you set up another break-point.
Still, coming from MATLAB, this seems the best solution I've found.
From python 3.2, you have the interact command, which gives you access to the full python/ipython command space.
Running from inside Emacs' IPython-shell and breakpoint set via pdb.set_trace() should work.
Checked with python-mode.el, M-x ipython RET etc.
Developing New Code
Debugging inside IPython
Use Jupyter/IPython cell execution to speed up experiment iterations
Use %%debug for step through
Cell Example:
%%debug
...: for n in range(4):
...: n>2
Debugging Existing Code
IPython inside debugging
Debugging a broken unit test: pytest ... --pdbcls=IPython.terminal.debugger:TerminalPdb --pdb
Debugging outside of test case: breakpoint(), python -m ipdb, etc.
IPython.embed() for full IPython functionality where needed while in the debugger
Thoughts on Python
I agree with the OP that many things MATLAB does nicely Python still does not have and really should since just about everything in the language favors development speed over production speed. Maybe someday I will contribute more than trivial bug fixes to CPython.
https://github.com/ipython/ipython/commit/f042f3fea7560afcb518a1940daa46a72fbcfa68
See also Is it possible to run commands in IPython with debugging?
If put import ipdb; ipdb.set_trace() at cell outside function, it will occur error.
Using %pdb or %debug, you can only see the filnal error result. You cannot see the code doing step by step.
I use following skill:
%%writefile temp.py
.....cell code.....
save the code of cell to file temp.py.
and then
%run -i -d temp.py, it will run the cell code by pdb .
-i: run the file in IPython’s namespace instead of an empty one.
-d: run your program under the control of pdb, the Python debugger.