Databases
StackOverflow2013
Postsdbo
POKeeping a pipe to a process open
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POKeeping a pipe to a process open
    primarykey
    data
    text
    <p>I have an <code>app</code> that reads in stuff from <code>stdin</code> and returns, after a newline, results to <code>stdout</code></p> <p>A simple (stupid) example:</p> <pre><code>$ app Expand[(x+1)^2]&lt;CR&gt; x^2 + 2*x + 1 100 - 4&lt;CR&gt; 96 </code></pre> <p>Opening and closing the <code>app</code> requires a lot of initialization and clean-up (its an interface to a Computer Algebra System), so I want to keep this to a minimum.</p> <p>I want to open a pipe in Python to this process, write strings to its <code>stdin</code> and read out the results from <code>stdout</code>. <code>Popen.communicate()</code> doesn't work for this, as it closes the file handle, requiring to reopen the pipe. </p> <p>I've tried something along the lines of this related question: <a href="https://stackoverflow.com/questions/3065060/communicate-multiple-times-with-a-process-without-breaking-the-pipe">Communicate multiple times with a process without breaking the pipe?</a> but I'm not sure how to wait for the output. It is also difficult to know a priori how long it will take the <code>app</code> to finish to process for the input at hand, so I don't want to make any assumptions. I guess most of my confusion comes from this question: <a href="https://stackoverflow.com/questions/375427/non-blocking-read-on-a-subprocess-pipe-in-python">Non-blocking read on a subprocess.PIPE in python</a> where it is stated that mixing high and low level functions is not a good idea.</p> <p><strong>EDIT</strong>: Sorry that I didn't give any code before, got interrupted. This is what I've tried so far and it seems to work, I'm just worried that something goes wrong unnoticed:</p> <pre><code>from subprocess import Popen, PIPE pipe = Popen(["MathPipe"], stdin=PIPE, stdout=PIPE) expressions = ["Expand[(x+1)^2]", "Integrate[Sin[x], {x,0,2*Pi}]"] # ... for expr in expressions: pipe.stdin.write(expr) while True: line = pipe.stdout.readline() if line != '': print line # output of MathPipe is always terminated by ';' if ";" in line: break </code></pre> <p>Potential problems with this?</p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USCommunity
    1. USbbtrb
    plurals
    1. PL
      singulars
      1. LTLinked
    2. PL
      singulars
      1. LTLinked
    3. PL
      singulars
      1. LTLinked
    1. PL
      singulars
      1. LTLinked
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POKeeping a pipe to a process open
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. POKeeping a pipe to a process open
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. POKeeping a pipe to a process open
      1. This table or related slice is empty.
      1. VTUpMod
    1. CO`process.stdout.write()` and `process.stdin.read()`
      singulars
      1. POKeeping a pipe to a process open
      1. USJakob Bowyer
    2. COWhile this looks like Mathematica, I asked a similar question earlier for MAPLE. Take a look at http://stackoverflow.com/questions/2053231/grabbing-the-output-of-maple-via-python
      singulars
      1. POKeeping a pipe to a process open
      1. USHooked
    3. CO@Hooked: Thanks for this. It looks like what I'm doing is in one of the answers to your question...
      singulars
      1. POKeeping a pipe to a process open
      1. USbbtrb
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload