@@ -21,7 +21,7 @@ Command line

When invoking Python, you may specify any of these options::

python [-bBdEhiOsSuvVWx?] [-c command | -m module-name | script | - ] [args]

python [-bBdEhiORsSuvVWx?] [-c command | -m module-name | script | - ] [args]

The most common use case is, of course, a simple invocation of a script::

@@ -215,6 +215,29 @@ Miscellaneous options

Discard docstrings in addition to the :option:`-O` optimizations.

.. cmdoption:: -R

Turn on hash randomization, so that the :meth:`__hash__` values of str, bytes

and datetime objects are "salted" with an unpredictable random value.

Although they remain constant within an individual Python process, they are

not predictable between repeated invocations of Python.

This is intended to provide protection against a denial-of-service caused by

carefully-chosen inputs that exploit the worst case performance of a dict

insertion, O(n^2) complexity. See

http://www.ocert.org/advisories/ocert-2011-003.html for details.

Changing hash values affects the order in which keys are retrieved from a

dict. Although Python has never made guarantees about this ordering (and it

typically varies between 32-bit and 64-bit builds), enough real-world code

implicitly relies on this non-guaranteed behavior that the randomization is

disabled by default.

See also :envvar:`PYTHONHASHSEED`.

.. versionadded:: 3.1.5

.. cmdoption:: -s

Don't add user site directory to sys.path

@@ -314,6 +337,7 @@ Miscellaneous options

.. note:: The line numbers in error messages will be off by one.

Options you shouldn't use

~~~~~~~~~~~~~~~~~~~~~~~~~

@@ -328,6 +352,7 @@ Options you shouldn't use

Reserved for alternative implementations of Python to use for their own

purposes.

.. _using-on-envvars:

Environment variables

@@ -435,6 +460,27 @@ These environment variables influence Python's behavior.

import of source modules.

.. envvar:: PYTHONHASHSEED

If this variable is set to ``random``, the effect is the same as specifying

the :option:`-R` option: a random value is used to seed the hashes of str,

bytes and datetime objects.

If :envvar:`PYTHONHASHSEED` is set to an integer value, it is used as a fixed

seed for generating the hash() of the types covered by the hash

randomization.

Its purpose is to allow repeatable hashing, such as for selftests for the

interpreter itself, or to allow a cluster of python processes to share hash

values.

The integer must be a decimal number in the range [0,4294967295]. Specifying

the value 0 will lead to the same hash values as when hash randomization is

disabled.

.. versionadded:: 3.1.5

.. envvar:: PYTHONIOENCODING

Overrides the encoding used for stdin/stdout/stderr, in the syntax