waylan · April 10, 2012 19:12 · Apr 11, 2012 · Apr 11, 2012 · Apr 11, 2012 · Apr 11, 2012
diff --git a/subprocess_pipe.md b/subprocess_pipe.md
@@ -71,7 +71,7 @@ for x in xrange(100):
     try:
         p.stdin.write(line)
     except IOError as e:
-        if e.errno = errno.EPIPE or e.errno = errno.EINVAL:
+        if e.errno == errno.EPIPE or e.errno == errno.EINVAL:
             # Stop loop on "Invalid pipe" or "Invalid argument".
             # No sense in continuing with broken pipe.
             break

diff --git a/subprocess_pipe.md b/subprocess_pipe.md
@@ -71,7 +71,7 @@ for x in xrange(100):
     try:
         p.stdin.write(line)
     except IOError as e:
-        if e.errno = errno.EPIPE and e.errno = errno.EINVAL:
+        if e.errno = errno.EPIPE or e.errno = errno.EINVAL:
             # Stop loop on "Invalid pipe" or "Invalid argument".
             # No sense in continuing with broken pipe.
             break

diff --git a/subprocess_pipe.md b/subprocess_pipe.md
@@ -71,13 +71,16 @@ for x in xrange(100):
     try:
         p.stdin.write(line)
     except IOError as e:
-        # Silently fail on "Invalid pipe" or "Invalid argument".
-        # Raise any other error.
-        if e.errno != errno.EPIPE and e.errno != errno.EINVAL:
+        if e.errno = errno.EPIPE and e.errno = errno.EINVAL:
+            # Stop loop on "Invalid pipe" or "Invalid argument".
+            # No sense in continuing with broken pipe.
+            break
+        else:
+            # Raise any other error.
             raise
 
 p.stdin.close()
 p.wait()
 
-print 'All done!'
+print 'All done!' # This should always be printed below any output written to less.
 ```
diff --git a/subprocess_pipe.md b/subprocess_pipe.md
@@ -56,4 +56,28 @@ except IOError as e:
         raise
 ```
 
-Note that [`errno.EPIPE`](http://docs.python.org/library/errno.html?highlight=errno#errno.EPIPE) is "Broken pipe" and [`errno.EINVAL`](http://docs.python.org/library/errno.html?highlight=errno#errno.EINVAL) is "Invalid argument".
+Note that [`errno.EPIPE`](http://docs.python.org/library/errno.html?highlight=errno#errno.EPIPE) is "Broken pipe" and [`errno.EINVAL`](http://docs.python.org/library/errno.html?highlight=errno#errno.EINVAL) is "Invalid argument". 
+
+So the final code looks like this:
+
+``` python
+
+from subprocess import Popen, PIPE
+import errno
+
+p = Popen('less', stdin=PIPE)
+for x in xrange(100):
+    line = 'Line number %d.\n' % x
+    try:
+        p.stdin.write(line)
+    except IOError as e:
+        # Silently fail on "Invalid pipe" or "Invalid argument".
+        # Raise any other error.
+        if e.errno != errno.EPIPE and e.errno != errno.EINVAL:
+            raise
+
+p.stdin.close()
+p.wait()
+
+print 'All done!'
+```
diff --git a/subprocess_pipe.md b/subprocess_pipe.md
@@ -30,4 +30,30 @@ for x in xrange(100):
 p.communicate('\n'.join(out))
 ```
 
-This works __great__! We only have one call to `communicate` and that calls `wait` properly. Unfortunately, we have to create the entire output in memory before writing any of it out. At least it works.
+This works. We only have one call to `communicate` and that calls `wait` properly. Unfortunately, we have to create the entire output in memory before writing any of it out. We can do better:
+
+```python
+from subprocess import Popen, PIPE
+
+p = Popen('less', stdin=PIPE)
+for x in xrange(100):
+    p.stdin.write('Line number %d.\n' % x)
+p.stdin.close()
+p.wait()
+```
+
+The key it to close stdin (flush and send EOF) before calling `wait`. This is actually what `communicate` does internally minus all the stdout and stderr stuff I don't need. If I wanted to force the buffer to remain empty, I suppose I could do `p.stdin.flush()` on each loop, but why? Note that there probably should be some error checking on write (like there is in the source of `communicate`. Perhaps something like:
+
+``` python
+import errno
+
+...
+
+try:
+    p.stdin.write(input)
+except IOError as e:
+    if e.errno != errno.EPIPE and e.errno != errno.EINVAL:
+        raise
+```
+
+Note that [`errno.EPIPE`](http://docs.python.org/library/errno.html?highlight=errno#errno.EPIPE) is "Broken pipe" and [`errno.EINVAL`](http://docs.python.org/library/errno.html?highlight=errno#errno.EINVAL) is "Invalid argument".
diff --git a/subprocess_pipe.md b/subprocess_pipe.md
@@ -26,7 +26,7 @@ from subprocess import Popen, PIPE
 out = []
 p = Popen('less', stdin=PIPE)
 for x in xrange(100):
-    out.append('Line number %d.\n' % x)
+    out.append('Line number %d.' % x)
 p.communicate('\n'.join(out))
 ```
 

diff --git a/subprocess_pipe.md b/subprocess_pipe.md
@@ -0,0 +1,33 @@
+Here's a few things I tried to write output to a python subprocess pipe.
+
+```python
+from subprocess import Popen, PIPE
+
+p = Popen('less', stdin=PIPE)
+for x in xrange(100):
+    p.communicate('Line number %d.\n' % x)
+```
+
+This seemed like the most obvious solution but it fails miserably. It seems that the first call to `communicate` also closes the pipe and the second loop raises an exception.
+
+```python
+from subprocess import Popen, PIPE
+
+p = Popen('less', stdin=PIPE)
+for x in xrange(100):
+    p.stdin.write('Line number %d.\n' % x)
+```
+
+This is expressly stated to be a bad idea in the docs, but it works - sort of. I get some weird behavior. There's no call to `p.wait()` (which `communicate` does by default) so anything after the loop runs before the subproccess (`less` in this case) is closed. Adding a call to `wait` after the loop causes even weirder behavior.
+
+```python
+from subprocess import Popen, PIPE
+
+out = []
+p = Popen('less', stdin=PIPE)
+for x in xrange(100):
+    out.append('Line number %d.\n' % x)
+p.communicate('\n'.join(out))
+```
+
+This works __great__! We only have one call to `communicate` and that calls `wait` properly. Unfortunately, we have to create the entire output in memory before writing any of it out. At least it works.
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