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[Q] ipython: Multiple commands on the same line and newlines

 
 
Phil Winder
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      04-16-2011
Hi,
I'm having a go at using ipython as a command prompt for data
analysis. Coming from Matlab, I'm used to typing multiple commands on
the same line then using the up arrow to go through my history.
How can I write multiple python commands on the same line?
E.g. "x = 0; while x < 10: x = x + 1;" returns an "invalid syntax"
error on the 'e' in while.

Also, how can I produce a new line, without it running the command? I
would have expected a ctrl-enter or shift-enter to produce the
expected results.
E.g. I want:
"x = 0; <ctrl-enter>
while x < 10: <ctrl-enter>
x = x + 1; <ctrl-enter>
" <enter to run>
It seems to work automatically for the "while xxx:", but combinations
of keys+enter do not work for "normal" lines.

Cheers,
Phil
 
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Andrea Crotti
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      04-16-2011
Phil Winder <(E-Mail Removed)> writes:

> Hi,
> I'm having a go at using ipython as a command prompt for data
> analysis. Coming from Matlab, I'm used to typing multiple commands on
> the same line then using the up arrow to go through my history.
> How can I write multiple python commands on the same line?
> E.g. "x = 0; while x < 10: x = x + 1;" returns an "invalid syntax"
> error on the 'e' in while.
>
> Also, how can I produce a new line, without it running the command? I
> would have expected a ctrl-enter or shift-enter to produce the
> expected results.
> E.g. I want:
> "x = 0; <ctrl-enter>
> while x < 10: <ctrl-enter>
> x = x + 1; <ctrl-enter>
> " <enter to run>
> It seems to work automatically for the "while xxx:", but combinations
> of keys+enter do not work for "normal" lines.
>
> Cheers,
> Phil


Well when you do something like

while x < 10:

it doesn't execute anything, but goes to newline and waits for the rest.

for
x = 10

what's the difference for you if it gets evaluated before or after?
Anyway you can you also %cpaste if you want to write more code

Anyway to me this works perfectly:
In [1]: x = 0

In [2]: while x < 10: print x; x += 1
...:
0
1
2
3
4
5
6
7
8
9

 
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Chris Angelico
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Posts: n/a
 
      04-16-2011
On Sun, Apr 17, 2011 at 2:29 AM, Andrea Crotti
<(E-Mail Removed)> wrote:
> for
> x = 10
>
> what's the difference for you if it gets evaluated before or after?


I have the same issue in IDLE sometimes, and the reason it's annoying
relates to the up-arrow key (Alt-P in IDLE). I can retrieve one entire
command, but if that command requires a "prefix statement" to set
things up (like initializing a dictionary to empty), that has to be
separate.

Chris Angelico
 
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Phil Winder
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      04-16-2011
On Apr 16, 5:29*pm, Andrea Crotti <(E-Mail Removed)> wrote:
> Phil Winder <(E-Mail Removed)> writes:
> > Hi,
> > I'm having a go at using ipython as a command prompt for data
> > analysis. Coming from Matlab, I'm used to typing multiple commands on
> > the same line then using the up arrow to go through my history.
> > How can I write multiple python commands on the same line?
> > E.g. "x = 0; while x < 10: x = x + 1;" returns an "invalid syntax"
> > error on the 'e' in while.

>
> > Also, how can I produce a new line, without it running the command? I
> > would have expected a ctrl-enter or shift-enter to produce the
> > expected results.
> > E.g. I want:
> > "x = 0; <ctrl-enter>
> > while x < 10: <ctrl-enter>
> > * * x = x + 1; <ctrl-enter>
> > " <enter to run>
> > It seems to work automatically for the "while xxx:", but combinations
> > of keys+enter do not work for "normal" lines.

>
> > Cheers,
> > Phil

>
> Well when you do something like
>
> while x < 10:
>
> it doesn't execute anything, but goes to newline and waits for the rest.
>
> for
> x = 10
>
> what's the difference for you if it gets evaluated before or after?
> Anyway you can you also %cpaste if you want to write more code
>
> Anyway to me this works perfectly:
> In [1]: x = 0
>
> In [2]: while x < 10: print x; x += 1
> * *...:
> 0
> 1
> 2
> 3
> 4
> 5
> 6
> 7
> 8
> 9


Yes, that does not produce an error, but it does not "work". Please
refer to my first post. Try the first code, you will get a syntax
error. Placing things on one line makes for easy history scrollback.
In your version you will have 2 lines of history for the x = 0 term
and the while ... term. I don't want to have to press up twice,
especially when the code was in the distant past! Also cpaste might be
ok for scripting, but it looks too clumsy to use at the command line.

Cheers,
Phil
 
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Terry Reedy
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Posts: n/a
 
      04-16-2011
On 4/16/2011 9:55 AM, Phil Winder wrote:
> Hi,
> I'm having a go at using ipython as a command prompt for data
> analysis. Coming from Matlab, I'm used to typing multiple commands on
> the same line then using the up arrow to go through my history.
> How can I write multiple python commands on the same line?


You can write multiple *simple* statements using ';'.

> E.g. "x = 0; while x< 10: x = x + 1;" returns an "invalid syntax"
> error on the 'e' in while.


All compound statements, like while, must start on own line.

> Also, how can I produce a new line, without it running the command?


Use an editor, as with IDLE, rather than a shell. Interactive mode runs
*1* statement (including simple;simple) at a time.

> would have expected a ctrl-enter or shift-enter to produce the
> expected results.
> E.g. I want:
> "x = 0;<ctrl-enter>


This is one statement

> while x< 10:<ctrl-enter>
> x = x + 1;<ctrl-enter>


This is another.

I can understanding wanting to rerun initialized loops with one enter,
but you cannot. Sorry.

--
Terry Jan Reedy

 
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OKB (not okblacke)
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Posts: n/a
 
      04-17-2011
Phil Winder wrote:

> Hi,
> I'm having a go at using ipython as a command prompt for data
> analysis. Coming from Matlab, I'm used to typing multiple commands on
> the same line then using the up arrow to go through my history.
> How can I write multiple python commands on the same line?
> E.g. "x = 0; while x < 10: x = x + 1;" returns an "invalid syntax"
> error on the 'e' in while.
>
> Also, how can I produce a new line, without it running the command? I
> would have expected a ctrl-enter or shift-enter to produce the
> expected results.
> E.g. I want:
> "x = 0; <ctrl-enter>
> while x < 10: <ctrl-enter>
> x = x + 1; <ctrl-enter>
> " <enter to run>
> It seems to work automatically for the "while xxx:", but combinations
> of keys+enter do not work for "normal" lines.


You might want to take a look at DreamPie (
http://dreampie.sourceforge.net/ ), which provides the second option you
indicate (and thus makesthe first unnecessary). I've found it quite
convenient for interactive use.


--
--OKB (not okblacke)
Brendan Barnwell
"Do not follow where the path may lead. Go, instead, where there is
no path, and leave a trail."
--author unknown
 
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Andrea Crotti
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Posts: n/a
 
      04-17-2011
Phil Winder <(E-Mail Removed)> writes:

> Yes, that does not produce an error, but it does not "work". Please
> refer to my first post. Try the first code, you will get a syntax
> error. Placing things on one line makes for easy history scrollback.
> In your version you will have 2 lines of history for the x = 0 term
> and the while ... term. I don't want to have to press up twice,
> especially when the code was in the distant past! Also cpaste might be
> ok for scripting, but it looks too clumsy to use at the command line.
>
> Cheers,
> Phil


Well I guess that's the way it is with the interpreter..
But I don't see the sense in doing everything from there, just write the
code to a file and use %edit from ipython to change and run it, it's
quite nice and easy too.
 
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Phil Winder
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Posts: n/a
 
      04-17-2011
On Apr 17, 1:11*pm, Andrea Crotti <(E-Mail Removed)> wrote:
> Phil Winder <(E-Mail Removed)> writes:
> > Yes, that does not produce an error, but it does not "work". Please
> > refer to my first post. Try the first code, you will get a syntax
> > error. Placing things on one line makes for easy history scrollback.
> > In your version you will have 2 lines of history for the x = 0 term
> > and the while ... term. I don't want to have to press up twice,
> > especially when the code was in the distant past! Also cpaste might be
> > ok for scripting, but it looks too clumsy to use at the command line.

>
> > Cheers,
> > Phil

>
> Well I guess that's the way it is with the interpreter..
> But I don't see the sense in doing everything from there, just write the
> code to a file and use %edit from ipython to change and run it, it's
> quite nice and easy too.


Ok, thanks all. It's a little disappointing, but I guess that you
always have to work in a different way when you move to a new
language. Andrea's %edit method is probably the best compromise, but
this now means that I will have to learn all the (obscure) shortcuts
for vi!

Cheers,
Phil
 
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Alexander Kapps
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Posts: n/a
 
      04-17-2011
On 17.04.2011 20:40, Phil Winder wrote:
> Ok, thanks all. It's a little disappointing, but I guess that you
> always have to work in a different way when you move to a new
> language. Andrea's %edit method is probably the best compromise, but
> this now means that I will have to learn all the (obscure) shortcuts
> for vi!


As you can read in "Python IDE/text-editor" thread. Learning either
Vim or Emacs will pay off in the long run,

Anyway, IPython honors the $EDITOR environment variable. Just set it
to whatever editor you prefer.

 
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harrismh777
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Posts: n/a
 
      04-18-2011
Terry Reedy wrote:
> You can write multiple *simple* statements using ';'.


> All compound statements, like while, must start on own line.


>> E.g. I want:
>> "x = 0;<ctrl-enter>

>
> This is one statement


>> while x< 10:<ctrl-enter>
>> x = x + 1;<ctrl-enter>



Lutz has a very nice write-up entitled "Why Indentation Syntax?"

Lutz, Mark, "Learning Python: Powerful Object Oriented Programming,"
4th ed, (Sebastopol: O'Reilly, 2009), 266 -271.

He makes the point clear that only simple statements may be chained
together on a single line with ; and that compound statements (like
while) "must still appear on lines of their own" (Lutz, 269).

It might be nice (as an option) to be able to disengage the forced
indentation syntax rules of Python. In other words, provide indentation
syntax by default and allow an option via environment variable to engage
an alternate (more C-like) blocking syntax.

The forced indentation syntax is great for readability (and
frankly, I like the appearance /low clutter) but it is inconvenient in
some situations, like the one at the top of the thread.

Just an idea (probably already been beaten to death long before my
time)

kind regards,
m harris


 
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