In Julia, calling a function with the #edit macro from the REPL will open the editor and put the cursor at the line where the method is defined. So, doing this:
julia> #edit 1 + 1
jumps to julia/base/int.jl and puts the cursor on the line:
(+)(x::T, y::T) where {T<:BitInteger} = add_int(x, y)
As does the function form: edit(+, (Int, Int))
Is there an equivalent decorator/function in Python that does the same from the Python REPL?
Disclaimer: In the Python ecosystem, this is not the job of the core language/runtime but rather tools such as IDEs. For example, the ipython shell has the ?? special syntax to get improved help including source code.
Python 3.8.5 (default, Jul 21 2020, 10:42:08)
Type 'copyright', 'credits' or 'license' for more information
IPython 7.18.1 -- An enhanced Interactive Python. Type '?' for help.
In [1]: import random
In [2]: random.uniform??
Signature: random.uniform(a, b)
Source:
def uniform(self, a, b):
"Get a random number in the range [a, b) or [a, b] depending on rounding."
return a + (b-a) * self.random()
File: /usr/local/Cellar/python#3.8/3.8.5/Frameworks/Python.framework/Versions/3.8/lib/python3.8/random.py
Type: method
The Python runtime itself allows viewing source code of objects via inspect.getsource. This uses a heuristic to search the source code as available; the objects themselves do not carry their source code.
Python 3.8.5 (default, Jul 21 2020, 10:42:08)
[Clang 11.0.0 (clang-1100.0.33.17)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import inspect
>>> print(inspect.getsource(inspect.getsource))
def getsource(object):
"""Return the text of the source code for an object.
The argument may be a module, class, method, function, traceback, frame,
or code object. The source code is returned as a single string. An
OSError is raised if the source code cannot be retrieved."""
lines, lnum = getsourcelines(object)
return ''.join(lines)
It is not possible to resolve arbitrary expressions or statements to their source; since all names in Python are resolved dynamically, the vast majority of expressions does not have a well-defined implementation unless executed. A debugger, e.g. as provided by pdb.set_trace(), allows inspecting the expression as it is executed.
In most IDEs like PyCharm or VSCode you can Ctrl+ click on a function / class to get its definition, even if it is in the core language or a 3rd party library (in VSCode, this also works in Julia btw.).
A limitation is that this only works for "pure Python" code, C library code, etc. is not shown.
Related
I'm sure it's intentional, so can someone explain the rationale for this behavior:
Python 2.7.2 (default, Oct 13 2011, 15:27:47)
[GCC 4.1.2 20080704 (Red Hat 4.1.2-44)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> from os.path import isdir,expanduser
>>> isdir("~amosa/pdb")
False
>>> isdir(expanduser("~amosa/pdb"))
True
>>>
>>> from os import chdir
>>> chdir("~amosa/pdb")
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
OSError: [Errno 2] No such file or directory: '~amosa/pdb'
>>> chdir(expanduser("~amosa/pdb"))
>>>
It's really annoying since, after all, the path with a username in it can be resolved unambiguously... I want to write code that can handle any sort of input that a user might give me, but this behavior requires me to call expanduser on every path my code has to deal with. It also means that anywhere I print that path out for the user to see, it will be slightly less legible than what they gave me.
This seems inconsistent with the concept of "duck typing" in which I generalize to mean that I expect python not to whine to me unless there's actually a problem...
Because the underlying system calls don't recognize user paths, and the file access APIs are a fairly thin wrapper over them.
Additionally, it would be fairly surprising for non-Unix users,
if (for example) fopen("~foo") returns a "foo: no such user" error (as "~foo" is a valid file name on, for example, Windows)…
Or, similarly, if fopen("~administrator") returns an error like "Is a directory: C:\Documents and Settings\Administrator\".
Finally, as commenters have noted: you're confusing "duck typing" with "helpful shortcuts", which are two entirely different things:
- Duck typing allows me to substitute for a duck anything which quacks like a duck.
- Helpful shortcuts allow me to substitute for a duck anything which could be made to quack like a duck.(Python does not "try to make it quack" like some other languages do).
In normal Unix utilities, the ~amosa syntax is handled by the shell, which is the program that invokes utilities. The utilities themselves do not know about the special ~ syntax (generally).
So if your python program is invoked by a shell on Unix, it will Just Work:
$ python -c 'import sys; print sys.argv[1]' ~drj
/home/drj
Notice how the python program above prints the expanded path, even though it clearly has no code to do the expansion itself. The shell expanded it.
Someone explain to me instead of verifying your python code program with some print function, it is suggested to use :
import lPython
lPython.embed()
As I don't have I lot of experience with python, could anyone be able to show me how it work with an example? And maybe how to understand each statement?
I believe you have a typo with IPython.
Here is an example:
a = 1
from IPython import embed # please notice the 'I' not the 'l'
embed()
c = 2
What this line of code does - it stops execution of your program and runs python session which allows you to introspect values. For instance if I run this code:
python tmp.py
It will stop the execution, run python and it will show you an ipython interpepator.
Python 2.7.13 (default, Dec 18 2016, 07:03:39)
Type "copyright", "credits" or "license" for more information.
IPython 5.1.0 -- An enhanced Interactive Python.
? -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help -> Python's own help system.
object? -> Details about 'object', use 'object??' for extra details.
In [1]:
If you type 'who' there you will list of all variables defined before ipython was called. See more information here: ipythondocs
however
I would strongly recommend to get familiar with pdb or ipdb.
Check documentation here pdbdocs. It is much more easier and gives you an ability of actual debugging of the code as in previous solution any changes you make - will not affect execution runtime.
My question is more theoretical than practical, I've found more answers that explains how but not why should we use a list in a subprocess.Popen call.
For example as is known:
Python 2.7.10 (default, Oct 14 2015, 16:09:02)
[GCC 5.2.1 20151010] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import subprocess
>>> cmd = subprocess.Popen(["python", "-V"], stdout=subprocess.PIPE)
Python 2.7.10
Then I was messing around in UNIX and found something interesting:
mvarge#ubuntu:~$ strace -f python -V 2>&1
execve("/usr/bin/python", ["python", "-V"], [/* 29 vars */]) = 0
Probably both execve and the list model that subprocess use are someway related, but can anyone give a good explanation for this?
Thanks in advance.
The underlying C-level representation is a *char [] array. Representing this as a list in Python is just a very natural and transparent mapping.
You can use a string instead of a list with shell=True; the shell is then responsible for parsing the command line into a * char [] array. However, the shell adds a number of pesky complexities; see the many questions for why you want to avoid shell=True for a detailed explanation.
The command line arguments argv and the environment envp are just two of many OS-level structures which are essentially a null-terminated arrays of strings.
A process is an OS level abstraction — to create a process, you have to use OS API that dictates what you should use. It is not necessary to use a list e.g., a string (lpCommandLine) is the native interface on Windows (CreateProcess()). POSIX uses execv() and therefore the native interface is a sequence of arguments (argv). Naturally, subprocess Python module uses these interfaces to run external commands (create new processes).
The technical (uninsteresting) answer is that in "why we must", the "must" part is not correct as Windows demonstrates.
To understand "why it is", you could ask the creators of CreateProcess(), execv() functions.
To understand "why we should" use a list, look at the table of contents for Unix (list) and Windows (string): How Command Line Parameters Are Parsed — the task that should be simple is complicated on Windows.
The main difference is that on POSIX the caller is responsible for splitting a command line into separate parameters. While on Windows the command itself parses its parameters. Different programs may and do use different algorithms to parse the parameters. subprocess module uses MS C runtime rules (subprocess.list2cmdline()), to combine args list into the command line. It is much harder for a programmer to understand how the parameters might be parsed on Windows.
What works
When calling IPython.embed(), one can pass banner1, banner2 or header to customize the message that appears before the interactive session, like this:
import IPython
IPython.embed(banner2="*** Welcome! ***")
With the result:
Python 2.7.6 (default, Jun 22 2015, 17:58:13)
Type "copyright", "credits" or "license" for more information.
IPython 3.2.1 -- An enhanced Interactive Python.
? -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help -> Python's own help system.
object? -> Details about 'object', use 'object??' for extra details.
*** Welcome! ***
In [1]:
What doesn't work
When using IPython.start_ipython(), instead of IPython.embed() in the invocation above, I couldn't find any parameters that would influence the banner, except display_banner=False to omit the it entirely.
The best I could do was to mangle argv, to change the configuration, like:
import sys, IPython
argv = (
sys.argv[1:] +
['--TerminalInteractiveShell.banner2=*** Welcome! ***']
)
IPython.start_ipython(argv=argv)
This is usable but looks contrived.
I suppose I could also inherit from IPython.ipapp.TerminalInteractiveShell in my code and override .banner1 or .banner2, but this feels like overkill.
The Question
All I want is a way to pass banner2 into IPython.start_ipython().
Is there a more straightforward way?
More Technical details
The use case is to create a script that starts an IPython console session with some pre-defined variables for controlling an application with a fairly involved setup. And explain how to use the setup.
Something like:
import sys, myapp, IPython
explain_usage_of_session = """
You can use session.blah() to frobnicate the foobaringo
"""
session = myapp.MyComplicatedSessionFactory(including=
configuration.params(from_file))
sys.exit(
IPython.start_ipython(user_ns=dict(session=session),
banner2=explain_usage_of_session)
)
Constraints
The more specific use-case is that this script is being generated automatically by buildout's zc.recipe.egg, which locates IPython.start_ipython using IPython [console_scripts] entry point, so I'm limited in the amount of customization I can actually pass into the script, and I can't use IPython.embed() directly.
The super duper plus specific use-case is that I'm actually using anybox.recipe.odoo, which wraps zc.recipe.egg. The end result is that I'm even more limited in how the script is built.
Basically I can just set the parameters that are passed into IPython.start_ipython() call as with the arguments option of zc.recipe.egg, and nothing else. In particular, I can't use the initialization option of zc.recipe.egg.
And I'd rather not have to write my own entry-point.
As #Thomas K said, you can create an IPython.Config instance and set the banner2:
from IPython import start_ipython
from traitlets.config.loader import Config
c = Config()
c.TerminalInteractiveShell.banner2 = '*** Welcome! ***'
start_ipython(config=c)
The result:
$ python start_with_banner.py
Python 2.7.11+ (default, Mar 30 2016, 21:00:42)
Type "copyright", "credits" or "license" for more information.
IPython 2.4.1 -- An enhanced Interactive Python.
? -> Introduction and overview of IPython's features.
%quickref -> Quick reference.
help -> Python's own help system.
object? -> Details about 'object', use 'object??' for extra details.
*** Welcome! ***
In [1]:
Ftr: the Config constructor accepts kwargs:
c = Config(TerminalInteractiveShell={'banner2': '*** Welcome! ***'})
Hth,
dtk
Update: For versions before ipython 5.x, you could directly from IPython import Config.
So I am running a Python script within which I am calling Python's debugger, PDB by writing:
import ipdb; ipdb.set_trace()
(iPython's version of PDB, though for the matter I don't think it makes a difference; I use it for the colored output only).
Now, when I get to the debugger I want to execute a multi-line statement such as an if clause or a for loop but as soon as I type
if condition:
and hit the return key, I get the error message *** SyntaxError: invalid syntax (<stdin>, line 1)
How can one execute multi-line statements within PDB? If not possible is there a way around this to still executing an if clause or a for loop?
You could do this while in pdb to launch a temporary interactive Python session with all the local variables available:
(pdb) !import code; code.interact(local=vars())
Python 2.6.5 (r265:79063, Apr 16 2010, 13:57:41)
[GCC 4.4.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
(InteractiveConsole)
>>>
When you're done, use Ctrl-D to return to the regular pdb prompt.
Just don't hit Ctrl-C, that will terminate the entire pdb session.
In python3 ipdb (and pdb) have a command called interact. It can be used to:
Start an interactive interpreter (using the code module) whose global namespace contains all the (global and local) names found in the current scope.
To use it, simply enter interact at the pdb prompt. Among other things, it's useful for applying code spanning multiple lines, and also for avoiding accidental triggering of other pdb commands.
My recommendation is to use IPython embedding.
ipdb> from IPython import embed; embed()
Inside the Python (2.7.1) interpreter or debugger (import pdb), you can execute a multi-line statement with the following syntax.
for i in range(5): print("Hello"); print("World"); print(i)
Note: When I'm inside the interpreter, I have to hit return twice before the code will execute. Inside the debugger, however, I only have to hit return once.
There is the special case if you want a couple of commands be executed when hitting a break point. Then there is the debugger command commands. It allows you to enter multiple lines of commands and then end the whole sequence with the end key word. More with (pdb) help commands.
I don't know if you can do this, that'd be a great feature for ipdb though. You can use list comprehensions of course, and execute simple multi-line expressions like:
if y == 3: print y; print y; print y;
You could also write some functions beforehand to do whatever it is you need done that would normally take multiple lines.