## PYTHONPLATLIBDIR 

If this is set to a non-empty string, it overrides the sys.platlibdir value. 

New in version 3.9. 

## PYTHONSTARTUP 

If this is the name of a readable file, the Python commands in that file are executed before the first prompt is displayed in interactive mode. The file is executed in the same namespace where interactive commands are executed so that objects defined or imported in it can be used without qualification in the interactive session. You can also change the prompts$_{sys.ps1}$ and$_{sys.ps2}$ and the hook$_{sys.__interactivehook__}$ in this file. 

Raises an auditing event$_{cpython.run_startup}$ with the filename as the argument when called on startup. 

## PYTHONOPTIMIZE 

If this is set to a non-empty string it is equivalent to specifying the$_{-O}$option. If set to an integer, it is equivalent to specifying -O multiple times. 

## PYTHONBREAKPOINT 

If this is set, it names a callable using dotted-path notation. The module containing the callable will be imported and then the callable will be run by the default implementation of sys.breakpointhook() which itself is called by built-in breakpoint() . If not set, or set to the empty string, it is equiva- lent to the value “pdb.set_trace”. Setting this to the string “0” causes the default implementation of$_{sys.}$ breakpointhook() to do nothing but return immediately. 

New in version 3.7. 

## PYTHONDEBUG 

If this is set to a non-empty string it is equivalent to specifying the$_{-d}$option. If set to an integer, it is equivalent to specifying$_{-d}$multiple times. 

## PYTHONOLDPARSER 

If this is set to a non-empty string, enable the traditional LL(1) parser. 

See also the$_{-X}$$_{oldparser}$option and PEP 617 . 

Deprecated since version 3.9, will be removed in version 3.10. 

## PYTHONINSPECT 

If this is set to a non-empty string it is equivalent to specifying the$_{-i}$option. 

This variable can also be modified by Python code using$_{os.environ}$ to force inspect mode on program termination. 

## PYTHONUNBUFFERED 

If this is set to a non-empty string it is equivalent to specifying the$_{-u}$option. 

## PYTHONVERBOSE 

If this is set to a non-empty string it is equivalent to specifying the$_{-v}$ option. If set to an integer, it is equivalent to specifying$_{-v}$ multiple times. 

## PYTHONCASEOK 

If this is set, Python ignores case in$_{import}$ statements. This only works on Windows and OS X. 

## PYTHONDONTWRITEBYTECODE 

If this is set to a non-empty string, Python won’t try to write$_{.pyc}$ files on the import of source modules. This is equivalent to specifying the$_{-B}$option. 

## PYTHONPYCACHEPREFIX 

If this is set, Python will write$_{.pyc}$ files in a mirror directory tree at this path, instead of in$_{__pycache__}$ directories within the source tree. This is equivalent to specifying the$_{-X}$$_{pycache_prefix=PATH}$option. 

New in version 3.8. 

## PYTHONHASHSEED 

If this variable is not set or set to$_{random}$, a random value is used to seed the hashes of str and bytes objects. 

