Python Pocket Reference, 3rd Edition

The os System Module

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popen4(cmd [, bufsize [, mode]])

Like popen3, but ties stdout and stderr to a single output

pipe. Returns the file object’s tuple:

(child_stdin, child_

stdout_and_stderr)

. New in Version 2.0.

See also the

subprocess module in Version 2.4 and later,

which allows you to spawn new processes, connect to their

input/output/error pipes, and obtain their return codes in

other ways.

Environment Tools

These attributes export execution environment and context.

environ

The shell environment variable dictionary. os.

environ['USER']

is the value of variable USER in the shell

(equivalent to

$USER in Unix and %USER% in DOS). Initial-

ized on program startup. Changes made to

os.environ by

key assignment are exported outside Python using a call

to C’s

putenv and are inherited by any processes that are

later spawned in any way, and any linked-in C code.

putenv(varname, value)

Sets the shell environment variable named varname to the

string

value. Affects subprocesses started with system,

popen, spawnv,orfork and execv. Assignment to os.

environ

keys automatically calls putenv (but putenv calls

don’t update

environ).

getcwd()

Returns the current working directory name as a string.

chdir(path)

Changes the current working directory for this process to

path, a directory name string. Future file operations are

relative to the new current working directory.

strerror(code)

Returns an error message corresponding to code ...