[Python-checkins] python/nondist/peps pep-0324.txt,1.3,1.4
effbot at users.sourceforge.net
effbot at users.sourceforge.net
Tue Oct 12 17:43:27 CEST 2004
Update of /cvsroot/python/python/nondist/peps
In directory sc8-pr-cvs1.sourceforge.net:/tmp/cvs-serv29270
Modified Files:
pep-0324.txt
Log Message:
Updated the subprocess PEP to the latest version.
Index: pep-0324.txt
===================================================================
RCS file: /cvsroot/python/python/nondist/peps/pep-0324.txt,v
retrieving revision 1.3
retrieving revision 1.4
diff -u -d -r1.3 -r1.4
--- pep-0324.txt 8 Oct 2004 13:03:22 -0000 1.3
+++ pep-0324.txt 12 Oct 2004 15:43:24 -0000 1.4
@@ -92,16 +92,16 @@
For example, many people cannot tell the difference between
popen2.popen2 and popen2.popen4 without using the documentation.
- - Two small utility functions are provided: subprocess.call() and
- subprocess.callv(). These aims to be an enhancement over
- os.system(), while still very easy to use:
+ - One small utility functions is provided: subprocess.call(). It
+ aims to be an enhancement over os.system(), while still very
+ easy to use:
- It does not use the Standard C function system(), which has
limitations.
- It does not call the shell implicitly.
- - No need for quoting; using a variable argument list.
+ - No need for quoting; using an argument list.
- The return value is easier to work with.
@@ -116,17 +116,6 @@
The motivation behind the call() function is simple: Starting a
process and wait for it to finish is a common task.
- The callv() function is identical to call(), except that each
- non-keyword argument is treated as a program argument. This
- gives a slightly nicer syntax. The drawback is that callv()
- does not allow specifying the program and it's arguments as a
- whitespace-separated string: The entire (first) string would be
- interpreted as the executable. The implementation of callv() is
- also very simple:
-
- def callv(*args, **kwargs):
- return Popen(args, **kwargs).wait()
-
While Popen supports a wide range of options, many users have
simple needs. Many people are using os.system() today, mainly
because it provides a simple interface. Consider this example:
@@ -137,10 +126,9 @@
subprocess.call(["stty", "sane", "-F", device])
- Some people feel that the list brackets are clumsy. With
- callv(), they are not needed:
+ or, if executing through the shell:
- subprocess.callv("stty", "sane", "-F", device)
+ subprocess.call("stty sane -F " + device, shell=True)
- The "preexec" functionality makes it possible to run arbitrary
code between fork and exec. One might ask why there are special
@@ -177,18 +165,23 @@
Arguments are:
- - args should be a sequence of program arguments. The program to
- execute is normally the first item in the args sequence, but can
- be explicitly set by using the executable argument.
-
- - On UNIX: the Popen class uses os.execvp() to execute the child
- program, which operates on sequences. If args is a string, it
- will be converted to a sequence using the cmdline2list method.
- Please note that syntax for quoting arguments is different from
- a typical UNIX shell. See the documentation of the cmdline2list
- method for more information.
-
- - On Windows: the Popen class uses CreateProcess() to execute the
+ - args should be a string, or a sequence of program arguments.
+ The program to execute is normally the first item in the args
+ sequence or string, but can be explicitly set by using the
+ executable argument.
+
+ On UNIX, with shell=False (default): In this case, the Popen
+ class uses os.execvp() to execute the child program. args
+ should normally be a sequence. A string will be treated as a
+ sequence with the string as the only item (the program to
+ execute).
+
+ On UNIX, with shell=True: If args is a string, it specifies the
+ command string to execute through the shell. If args is a
+ sequence, the first item specifies the command string, and any
+ additional items will be treated as additional shell arguments.
+
+ On Windows: the Popen class uses CreateProcess() to execute the
child program, which operates on strings. If args is a
sequence, it will be converted to a string using the
list2cmdline method. Please note that not all MS Windows
@@ -221,11 +214,7 @@
will be closed before the child process is executed.
- If shell is true, the specified command will be executed through
- the shell. Note: When executing through the shell on UNIX
- systems and the args argument is a sequence, only the first
- element in the sequence will be passed as a command string to
- the shell. The remaining arguments can be used to specify
- additional shell options.
+ the shell.
- If cwd is not None, the current directory will be changed to cwd
before the child is executed.
@@ -261,21 +250,6 @@
retcode = call(["ls", "-l"])
- - callv(*args, **kwargs):
- Run command with arguments. Wait for command to complete,
- then return the returncode attribute.
-
- This function is identical to call(), except that each
- non-keyword argument is treated as a program argument.
- Example:
-
- retcode = callv("ls", "-l")
-
- This is equivalent to:
-
- retcode = call(["ls", "-l"])
-
-
Exceptions
----------
@@ -389,7 +363,7 @@
sts = os.system("mycmd" + " myarg")
==>
- p = Popen(["mycmd" + " myarg"], shell=True)
+ p = Popen("mycmd" + " myarg", shell=True)
sts = os.waitpid(p.pid, 0)
Note:
@@ -402,7 +376,7 @@
A more real-world example would look like this:
try:
- retcode = callv("mycmd", "myarg")
+ retcode = call("mycmd" + " myarg", shell=True)
if retcode < 0:
print >>sys.stderr, "Child was terminated by signal", -retcode
else:
@@ -425,7 +399,7 @@
retcode = os.spawnlp(os.P_WAIT, "/bin/mycmd", "mycmd", "myarg")
==>
- retcode = callv("/bin/mycmd", "myarg")
+ retcode = call(["/bin/mycmd", "myarg"])
Vector example:
@@ -447,16 +421,16 @@
pipe = os.popen(cmd, mode='r', bufsize)
==>
- pipe = Popen([cmd], shell=True, bufsize=bufsize, stdout=PIPE).stdout
+ pipe = Popen(cmd, shell=True, bufsize=bufsize, stdout=PIPE).stdout
pipe = os.popen(cmd, mode='w', bufsize)
==>
- pipe = Popen([cmd], shell=True, bufsize=bufsize, stdin=PIPE).stdin
+ pipe = Popen(cmd, shell=True, bufsize=bufsize, stdin=PIPE).stdin
(child_stdin, child_stdout) = os.popen2(cmd, mode, bufsize)
==>
- p = Popen([cmd], shell=True, bufsize=bufsize,
+ p = Popen(cmd, shell=True, bufsize=bufsize,
stdin=PIPE, stdout=PIPE, close_fds=True)
(child_stdin, child_stdout) = (p.stdin, p.stdout)
@@ -465,7 +439,7 @@
child_stdout,
child_stderr) = os.popen3(cmd, mode, bufsize)
==>
- p = Popen([cmd], shell=True, bufsize=bufsize,
+ p = Popen(cmd, shell=True, bufsize=bufsize,
stdin=PIPE, stdout=PIPE, stderr=PIPE, close_fds=True)
(child_stdin,
child_stdout,
@@ -474,7 +448,7 @@
(child_stdin, child_stdout_and_stderr) = os.popen4(cmd, mode, bufsize)
==>
- p = Popen([cmd], shell=True, bufsize=bufsize,
+ p = Popen(cmd, shell=True, bufsize=bufsize,
stdin=PIPE, stdout=PIPE, stderr=STDOUT, close_fds=True)
(child_stdin, child_stdout_and_stderr) = (p.stdin, p.stdout)
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