1. posix
— The most common POSIX system calls¶
This module provides access to operating system functionality that is standardized by the C Standard and the POSIX standard (a thinly disguised Unix interface).
Do not import this module directly. Instead, import the module os
,
which provides a portable version of this interface. On Unix, the os
module provides a superset of the posix
interface. On non-Unix operating
systems the posix
module is not available, but a subset is always
available through the os
interface. Once os
is imported, there is
no performance penalty in using it instead of posix
. In addition,
os
provides some additional functionality, such as automatically calling
putenv()
when an entry in os.environ
is changed.
Errors are reported as exceptions; the usual exceptions are given for type
errors, while errors reported by the system calls raise OSError
.
1.1. Large File Support¶
Several operating systems (including AIX, HP-UX, Irix and Solaris) provide
support for files that are larger than 2 GB from a C programming model where
int
and long
are 32-bit values. This is typically accomplished
by defining the relevant size and offset types as 64-bit values. Such files are
sometimes referred to as large files.
Large file support is enabled in Python when the size of an off_t
is
larger than a long
and the long long
type is available and is
at least as large as an off_t
. Python longs are then used to represent
file sizes, offsets and other values that can exceed the range of a Python int.
It may be necessary to configure and compile Python with certain compiler flags
to enable this mode. For example, it is enabled by default with recent versions
of Irix, but with Solaris 2.6 and 2.7 you need to do something like:
CFLAGS="`getconf LFS_CFLAGS`" OPT="-g -O2 $CFLAGS" \
./configure
On large-file-capable Linux systems, this might work:
CFLAGS='-D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64' OPT="-g -O2 $CFLAGS" \
./configure
1.2. Notable Module Contents¶
In addition to many functions described in the os
module documentation,
posix
defines the following data item:
-
posix.
environ
¶ A dictionary representing the string environment at the time the interpreter was started. For example,
environ['HOME']
is the pathname of your home directory, equivalent togetenv("HOME")
in C.Modifying this dictionary does not affect the string environment passed on by
execv()
,popen()
orsystem()
; if you need to change the environment, passenviron
toexecve()
or add variable assignments and export statements to the command string forsystem()
orpopen()
.