execution environment the - option starts an interactive session immediately after program has finished execution and is useful for debugging the - option runs library module as script which executes inside the _main_ module prior to the execution of the main script the - and -oo options apply some optimization to byte-compiled files and are described in "modulespackagesand distribution "the - option omits the site initialization module described in the later section "site configuration files the - -ttand - options report additional warnings and debugging information - ignores the first line of program in the event that it' not valid python statement (for examplewhen the first line starts the python interpreter in scriptthe program name appears after all the interpreter options if no name is givenor the hyphen (-character is used as filenamethe interpreter reads the program from standard input if standard input is an interactive terminala banner and prompt are presented otherwisethe interpreter opens the specified file and executes its statements until an end-of-file marker is reached the - cmd option can be used to execute short programs in the form of command-line option--for examplepython - "print('hello world')command-line options appearing after the program name or hyphen (-are passed to the program in sys argvas described in the section "reading options and environment variablesin "input and output additionallythe interpreter reads the following environment variablestable interpreter environment variables environment variable description pythonpath pythonstartup pythonhome pythoninspect pythonunbuffered pythonioencoding colon-separated module search path file executed on interactive startup location of the python installation implies the - option implies the - option encoding and error handling for stdinstdoutand stderr this is string of the form "encoding[:errors]such as "utf- or "utf :ignoreimplies the - option implies the - option implies the - option implies the - option root directory for per-user site packages indicates to use case-insensitive matching for module names used by import pythondontwritebytecode pythonoptimize pythonnousersite pythonverbose pythonuserbase pythoncaseok pythonpath specifies module search path that is inserted into the beginning of sys pathwhich is described in pythonstartup specifies file to execute when the interpreter runs in interactive mode the pythonhome variable is used to set the location of the python installation but is rarely needed because python knows how lib fl ff