I want to know how to refresh the console of my program as if it was just started. Let's say that my code consists of an infinite loop and it has multiple instances of the print() function within itself, I want, every time that loops returns to its start, all the new data whether there is some change or not to get outputted on the same place of the data that has been outputted the last time.
I have been reading about similar problems others have posted and the answers usually revolve around the idea of using \r, when I do that, however, it's always messy and the strings are either printed halfway or there are missing characters. On Replit there is a module called "replit" and there is a function there called clear() that basically performs what I need, but I don't seem to find it when I am using PyCharm, which means that it is perhaps something that works exclusively within the Replit environment. So I am asking, is there something similar in the standard python library that I can use? Thanks
You can use:
import os
command = 'cls' #for windows
os.system(command)
example:
print('hi')
os.system(command)
print('hi')
Output:
hi
For windows you need:
command = 'cls'
For all others it is:
command = 'clear'
To account for any OS you could use:
import os
def clearConsole():
command = 'clear'
if os.name in ('nt', 'dos'): # If computer is running windows use cls
command = 'cls'
os.system(command)
clearConsole()
There is nothing standard in Python to do it, because Python is not aware of whatever console you are using.
When you call print it is actually writing to a file called "standard output".
It can go to a console if you are running your program in a console (like windows cmd, Linux or Mac OS terminal app, or whatever PyCharm uses).
But it can also be redirected to a regular file by the user of your program.
So there is no standard way.
\r is "carriage return" character. On consoles that respect it, it will set your output position to the beginning of the current line, but will not erase any text already printed on that line (usually).
One way to print text in specific places on the screen is PyCurses.
It supports many consoles and figures out which one you are using automatically.
You can do something like this:
import curses
stdscr = curses.initscr()
stdscr.addstr(x, y, "my string")
By using the addstr isntead of print, you can choose the exact position the text will appear, with X and Y coordinates (first two parameters).
Read the documentation for more ways to manipulate text display with this library.
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.
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.
I have the following file. Why does code completion not run when I press Ctrl-Space after the "r."? It says "no suggestion" in a red box.
(The program as it is runs and puts out: 200)
__author__ = 'hape'
import urllib.request
import urllib.response
print("Starting")
r = urllib.request.urlopen("http://www.python.org")
r. <------------ No code completion, why not?!
print (r.getcode())
After the r., code completion does not popup, why?
Have you looked at the Pycharm page for Editor code completion settings?
http://www.jetbrains.com/pycharm/webhelp/editor-code-completion.html
By Enabling Smart Type code completion?
http://www.jetbrains.com/pycharm/webhelp/smart-type-code-completion-completing-code-based-on-type-information.html
Adding response from JetBrains:
#CrazyCoder was right there. The problem is that we are not able to infer proper return type of the function "urllib.request.urlopen()" since its implementation uses some dynamic tricks that we cannot handle statically, in particular:
Normally, we deal with difficult cases like that using external annotations in python-skeletons but it doesn't contain type hints for "urllib.request" module yet. Also in the upcoming versions of PyCharm we're planning to switch to the collection of annotations gathered in typeshed project. It evolves much more actively and already contains some annotations for "urllib". To benefit from them you just need to drop "urllib" package with annotations somewhere in your interpreter paths, so that PyCharm could find the respective .pyi stubs.
Check whether the IDE is in Power Saving Mode. If it is, then no code completion process or any any other background process works
It shows about it in the status bar at the bottom of the IDE
#CrazyCoder was right.Fow now, Pycharm does not kown the type of r.
If you really like to auto completion, first get the type of r using IPython or debug
# IPython
In [1]: import urllib.request
In [2]: r = urllib.request.urlopen("http://www.python.org")
In [3]: type(r)
Out[3]: http.client.HTTPResponse
then use Python3 Annotations
r: http.client.HTTPResponse = urllib.request.urlopen("http://www.python.org")
r.
Now, you can get
python annotation for http.client.HTTPResponse
I'm not sure if what I'm asking is possible at all, but since python is an interpreter it might be. I'm trying to make changes in an open-source project but because there are no types in python it's difficult to know what the variables have as data and what they do. You can't just look up the documentation on the var's type since you can't be sure what type it is. I want to drop to the terminal so I can quickly examine the types of the variables and what they do by typing help(var) or print(var). I could do this by changing the code and then re-running the program each time but that would be much slower.
Let's say I have a program:
def foo():
a = 5
my_debug_shell()
print a
foo()
my_debug_shell is the function I'm asking about. It would drop me to the '>>>' shell of the python interpreter where I can type help(a), and it would tell me that a is an integer. Then I type 'a=7', and some 'continue' command, and the program goes on to print 7, not 5, because I changed it.
http://docs.python.org/library/pdb.html
import pdb
pdb.set_trace()
Here is a solution that doesn't require code changes:
python -m pdb prog.py <prog_args>
(pdb) b 3
Breakpoint 1 at prog.py:3
(pdb) c
...
(pdb) p a
5
(pdb) a=7
(pdb) ...
In short:
start your program under debugger control
set a break point at a given line of code
let the program run up to that point
you get an interactive prompt that let's you do what you want (type 'help' for all options)
Python 3.7 has a new builtin way of setting breakpoints.
breakpoint()
The implementation of breakpoint() will import pdb and call pdb.set_trace().
Remember to include the braces (), since breakpoint is a function, not a keyword.
A one-line partial solution is simply to put 1/0 where you want the breakpoint: this will raise an exception, which will be caught by the debugger. Two advantages of this approach are:
Breakpoints set this way are robust against code modification (no dependence on a particular line number);
One does not need to import pdb in every program to be debugged; one can instead directly insert "breakpoints" where needed.
In order to catch the exception automatically, you can simply do python -m pdb prog.py… and then type c(ontinue) in order to start the program. When the 1/0 is reached, the program exits, but variables can be inspected as usual with the pdb debugger (p my_var). Now, this does not allow you to fix things and keep running the program. Instead you can try to fix the bug and run the program again.
If you want to use the powerful IPython shell, ipython -pdb prog.py… does the same thing, but leads to IPython's better debugger interface. Alternatively, you can do everything from within the IPython shell:
In IPython, set up the "debug on exception" mode of IPython (%pdb).
Run the program from IPython with %run prog.py…. When an exception occurs, the debugger is automatically activated and you can inspect variables, etc.
The advantage of this latter approach is that (1) the IPython shell is almost a must; and (2) once it is installed, debugging can easily be done through it (instead of directly through the pdb module). The full documentation is available on the IPython pages.
You can run the program using pdb, and add breakpoints before starting execution.
In reality though, it's usually just as fast to edit the code and put in the set_trace() call, as another user stated.
Not sure what the real question is. Python gives you the 'pdb' debugger (google yourself) and in addition you can add logging and debug output as needed.