Okay, so let me just say beforehand: I am new to Python. I was just experimenting with IDLE and then I had this weird "crash". I put "crash" inside speech marks because I'm not sure if it qualifies as a crash, as rather than the program just crashing the way a normal program would in Windows, it still runs, but whenever I press enter and try and get it to accept new text it doesn't do anything. E.g. if you try and type "print('a')" and then hit enter it just goes to the next line (and doesn't print 'a'). I tried to make a simple function which converted an integer to a string where each character in the string was either a '1' or a '0', forming the binary number representing said (unsigned) integer.
>>> def int_to_str(int_in):
str_out=''
bit_val=1<<int_in.bit_length()
while(int_in>0):
if(int_in>bit_val):
str_out+='1'
int_in-=bit_val
else:
str_out+='0'
bit_val>>=1
return str_out
>>> print('a')
print('c')
Basically, it becomes completely unresponsive to my input, and allows me to edit/change "print('a')" even though I shouldn't be able to if it had actually "accepted" my input. Why is this? What have I done wrong/messed up?
Also, I made sure it isn't something else I was previously messing around with by closing the shell and opening it again and only putting in said code for the "int_to_string" function, and I haven't changed any settings or imported any modules before hand or anything like that (in case it matters).
EDIT: I tried reinstalling, and that helped a bit in that I can now do other stuff fine, but the moment I try to use the "str_to_int()" function, it has this same weird behaviour of not accepting/interpreting any more user input.
Your while loop never terminates, you need to re-arrange your logic. Printing variables can be an effective debugging tool - like this:
>>> def int_to_str(int_in):
str_out=''
bit_val=1<<int_in.bit_length()
while(int_in>0):
print(int_in, bit_val)
if(int_in>bit_val):
str_out+='1'
int_in-=bit_val
else:
str_out+='0'
bit_val>>=1
return str_out
If your program seems to be going on too long you can stop it with ctrl-c.
Related
You will see in the screenshot that pressing enter after pasting a multiline code doesnt run it but merely send each time a "...".
How can I run this multiline pasted code?
someone asked here, but did not get (the right) answer;
Did not work:
Backspace
Use the arrow key to move the cursor, then use the delete key
Escape
F2
Pressing enter twice when inside the Python interpreter executes a block of code, but you have an unmatched open parenthesis on the last line, so you haven't completed defining the block of code. Also, I'm not sure what dic is in the last line, because you haven't included its definition, so you may need to fix that as well.
Running
a=[1,2]
for x in a:
print(x)
actually works (pressing 2 enters worked as expected). So I made a mistake in the code above. I aplogise, I should have checked that before.
I don't delete the question since the one on google can be confusing (the guy did not mentioned it was his mistake, so I though there was a trick to be found. The trick is to check the code).
you could use IPython link which simplifies the process, better yet you have access to every command line as if executed inside the shell.
The other alternative is to encapsulate this inside a function
I know this answer is a bit late, but someone will need the information sometime:
When you make a new line, i.e. title.quote.... you need to press the tab to create an indent, then it will work. Without indenting, you get the "expected an indent" error message.
I just finished watching this video https://www.youtube.com/watch?v=qO4ZN5uZSVg, and even though it teaches 2.0 edition Python, some notes pop up for the 3.0 uses of python. Nevertheless, in the end, some challenges are provided, one of them is this:
def returnTwo():
return 20,30
x,y = returnTwo()
print(x,y)
Whenever i try to see what the conclusion will be, this is what comes up
def returnTwo():
return 20,30
(red X in the 3.5 Shell) x,y = returnTwo()
SyntaxError: invalid syntax.
What can I do?
The python shell allows to interactively run commands. This is very useful when doing quick calculations of to quickly check some small pieces of code.
In this case, you want to define a function. Defining a function is just that: a definition. Later on, you actually call the function and make it run. The issue here is that a function is (often) defined in more than one line. That means, you actually hit enter before you finish to define the function. For that reason, you tell the shell that you finished with an extra enter:
This also applies if you define your function in a single line:
And that's the reason why you get a SyntaxError: The line x, y = returnTwo() is supposed to be in the function, but for that, it would need to indented (to the level of return 20, 30):
Like #jim said, just try pressing enter until you get the >>> prompt again!
Remember that the three little dots do have a meaning too.
This question was already answered in the comments by #helios35 and #jim!
I just elaborate and post as an answer here for future users.
This is a bit of an odd question; it came up in the context of a tool that exposes a Python API, which we spend a lot of time querying interactively from the REPL. The particular idiom causing issues is something like this:
for var in slow_generator_of_giant_list():
stats = update(stats, var)
print stats
To enter this at the REPL, I can type this:
>>> for var in slow_generator_of_giant_list():
... stats = update(stats, var)
...
If I now attempt to type the print, I get a syntax error due to improper indentation. (Or else I put the print inside the loop and do it on every iteration.)
But if I hit enter to go to the next line, the loop runs immediately, and I have to wait for it to finish, or type the print command in the face of possible output coming at me, etc.
Obviously I can define a function containing the above, and it might be worth saving into a file anyway, but in the general case we're constructing these on the fly, and it would be nice to have a way to "schedule" a command to run after the end of a loop from the REPL. In a language with block delimiters, I could of course put it after the ending delimiter (and any necessary statement separator). But my coworkers and I were stumped trying to do something similar here.
Is there perhaps an ugly abuse of Pythonic syntax that will do the trick that my coworkers and I couldn't think of? Or a recommended way to avoid the problem while still making it easy to throw together ad hoc interactive queries?
Thanks for any pointers.
Not beautiful, but this should work:
>>> mygen = slow_generator_of_giant_list()
>>> try:
... while True: stats = update(stats, mygen.next())
... except StopIteration:
... print stats
...
I would just say that you would find it easier just to not use the interactive shell for this.
It's not much effort to save a file and run it. You only have to keep it around for as long as you use it.
I actually have found this answering on SO. I keep a file open in my text editor with a terminal in the right directory, and just use it as a scratchpad for mocking up answers in.
I was writing a little program that takes a list and generates a menu out of it in curses (straight up, standard library or whatever, batteries included python's curses) when I noticed the strangest problem (if you'd like, a heavily commented copy of the entire program is below). Simply put, when accepting the results of an os.listdir generated list, curses crashes with an addstr ERR, BUT, if I feed it a hardcoded list, it works fine. This, of course, makes absolutely no sense, right? A list is a list is a list and a list by any other name should still be a list, right?
To make things even more complicated, I sent the code to a friend of mine who works mainly in python2.6 (mine was originally written to work in python3.1). He uncommented the broken_input() call (which feeds the program the os.listdir generated information) and said that it worked fine for him. I have both python 2.6 and 3.1 installed, so I changed my shebang to make the program run in 2.6, and (with the broken_input() uncommented) for me, it still throws the addstr ERR (yet runs fine with the hardcoded input... which is, of course, btw, entirely useless apart from proof of concept).
Thus, my question is this: is there something broken in my python installation (I'm running Ubuntu lucid, with python2.6.5 and 3.1 installed), and, if so, how do I fix it so I can get curses to execute this code properly. And, if it's not my python installation, how can I get the same functionality out of curses (i.e.: paint a menu from a list containing an arbitrary number of items, numbering them so that the user can make a selection based on the item number).
#!/usr/bin/env python3.1
"""curses_mp3eater.py: a curses-based implementation of my mp3eater program;
diplays the contents of cwd, allows user to make a selection. But I'm having
problems getting it to iterate over a list.
v0.1 03.14.11
by skookie sprite
address#gmail.com
"""
import curses, curses.wrapper, os, sys
def working_input():
"""the following is demo code to demonstrate my problem... main will accept the following,
but won't accept the product of a directorylist for reasons that I can't figure out."""
dircontents=['this','is','a','list','','and','it','will','iterate','fine','in','the','(main) function.']
return dircontents
def broken_input():
"""this is the code that I NEED to have work... but for reasons beyond me will not iterate in
the main function. It's a simple list of the contents of the CWD."""
cwd=os.getcwd()
dircontents=[]
for item in os.listdir(cwd):
dircontents += [item]
return dircontents
def main(stdscr):
"""This is the program. Designed to take a list of stuff and display it. If I can solve
that hurdle, I'll add selection mechanisms, and break it across screens - amongst other
things. But, currently, it can only accept the demo code. Uncomment one or the other to
see what I mean."""
#broken_input returns an addstr() ERR, but I don't see the difference between working_input
#and broken_input as they are both just lists.
#working_input() is demo code that illustrates my problem
stuffin=working_input()
#stuffin=broken_input()
#the rest of this stuff works. The problem is with the input. Why?
linenumber=int()
linenumber=6
itemnumber=int()
itemnumber=1
stdscr.clear()
stdscr.border(0)
for item in stuffin:
stdscr.addstr(linenumber, 10, '%s - %s' % (itemnumber, item), curses.A_NORMAL)
linenumber += 1
itemnumber += 1
curses.doupdate()
stdscr.getch()
if __name__ == '__main__':
curses.wrapper(main)
You're stuffing too much onto the screen and thus passing an out-of-bounds line number to addstr. If you make an empty directory to run the program in (or enlarge your terminal window), it works.
To fix this, check the number of lines in the window before the output loop in main.
use screen.scrollok(1) after addstr to allow the text to scroll.
The problem is explained in the addch manual page:
The addch, waddch, mvaddch and mvwaddch routines put the character ch
into the given window at its current window position, which is then
advanced. They are analogous to putchar(3) in stdio(3). If the
advance is at the right margin:
The cursor automatically wraps to the beginning of the next line.
At the bottom of the current scrolling region, and if scrollok is
enabled, the scrolling region is scrolled up one line.
If scrollok is not enabled, writing a character at the lower right
margin succeeds. However, an error is returned because it is not
possible to wrap to a new line
The given program neither catches an error from the lower right margin (probably should say "corner"), nor calls scrollok to allow the data to scroll up. In the latter case, you will lose information which is scrolled up, while handling the exception would allow you to prompt after a screen's worth of data is displayed, and then either quit or display more data.
Sometimes I'll be working with, say, a list of thousands of items in IDLE, and accidently print it out to the shell. When this happens, it crashes or at least very significaly slows down IDLE. As you can imagine, this is extremely inconvenient.
Is there a way to make it, rather than printing the entire thing, just give me a summarised [1, 2, ...] output?
Any help would be much appreciated.
As above, try a custom print function like:
def my_print(obj):
if hasattr(obj, '__len__') and len(obj) > 100:
print '... omitted object of %s with length %d ...' % (type(obj), len(obj))
else: print obj
Use IPython as shell instead.
You could use custom print function.
In Python 3, since print is a function, you should be able to "override" it. (I don't have it installed so I can't try it out to make sure.) Probably not recommended for real applications but if you're just trying things out, it would be okay I suppose.
It would go something like:
def myprint(*args):
# write the function as described by other people
print = myprint
The Squeezer extension for IDLE was written to do just this. From the description on Pypi:
IDLE can hang if very long output is printed. To avoid this, the Squeezer
extensions catches any output longer than 80 lines of text (configurable) and
displays a rectangular box instead:
Squeezer, and many other IDLE extensions are included in IdleX.