1 .. _tut-appendix: 2 3 ******** 4 Appendix 5 ******** 6 7 8 .. _tut-interac: 9 10 Interactive Mode 11 ================ 12 13 .. _tut-error: 14 15 Error Handling 16 -------------- 17 18 When an error occurs, the interpreter prints an error message and a stack trace. 19 In interactive mode, it then returns to the primary prompt; when input came from 20 a file, it exits with a nonzero exit status after printing the stack trace. 21 (Exceptions handled by an :keyword:`except` clause in a :keyword:`try` statement 22 are not errors in this context.) Some errors are unconditionally fatal and 23 cause an exit with a nonzero exit; this applies to internal inconsistencies and 24 some cases of running out of memory. All error messages are written to the 25 standard error stream; normal output from executed commands is written to 26 standard output. 27 28 Typing the interrupt character (usually :kbd:`Control-C` or :kbd:`Delete`) to the primary or 29 secondary prompt cancels the input and returns to the primary prompt. [#]_ 30 Typing an interrupt while a command is executing raises the 31 :exc:`KeyboardInterrupt` exception, which may be handled by a :keyword:`try` 32 statement. 33 34 35 .. _tut-scripts: 36 37 Executable Python Scripts 38 ------------------------- 39 40 On BSD'ish Unix systems, Python scripts can be made directly executable, like 41 shell scripts, by putting the line :: 42 43 #!/usr/bin/env python 44 45 (assuming that the interpreter is on the user's :envvar:`PATH`) at the beginning 46 of the script and giving the file an executable mode. The ``#!`` must be the 47 first two characters of the file. On some platforms, this first line must end 48 with a Unix-style line ending (``'\n'``), not a Windows (``'\r\n'``) line 49 ending. Note that the hash, or pound, character, ``'#'``, is used to start a 50 comment in Python. 51 52 The script can be given an executable mode, or permission, using the 53 :program:`chmod` command. 54 55 .. code-block:: bash 56 57 $ chmod +x myscript.py 58 59 On Windows systems, there is no notion of an "executable mode". The Python 60 installer automatically associates ``.py`` files with ``python.exe`` so that 61 a double-click on a Python file will run it as a script. The extension can 62 also be ``.pyw``, in that case, the console window that normally appears is 63 suppressed. 64 65 66 .. _tut-startup: 67 68 The Interactive Startup File 69 ---------------------------- 70 71 When you use Python interactively, it is frequently handy to have some standard 72 commands executed every time the interpreter is started. You can do this by 73 setting an environment variable named :envvar:`PYTHONSTARTUP` to the name of a 74 file containing your start-up commands. This is similar to the :file:`.profile` 75 feature of the Unix shells. 76 77 This file is only read in interactive sessions, not when Python reads commands 78 from a script, and not when :file:`/dev/tty` is given as the explicit source of 79 commands (which otherwise behaves like an interactive session). It is executed 80 in the same namespace where interactive commands are executed, so that objects 81 that it defines or imports can be used without qualification in the interactive 82 session. You can also change the prompts ``sys.ps1`` and ``sys.ps2`` in this 83 file. 84 85 If you want to read an additional start-up file from the current directory, you 86 can program this in the global start-up file using code like ``if 87 os.path.isfile('.pythonrc.py'): exec(open('.pythonrc.py').read())``. 88 If you want to use the startup file in a script, you must do this explicitly 89 in the script:: 90 91 import os 92 filename = os.environ.get('PYTHONSTARTUP') 93 if filename and os.path.isfile(filename): 94 with open(filename) as fobj: 95 startup_file = fobj.read() 96 exec(startup_file) 97 98 99 .. _tut-customize: 100 101 The Customization Modules 102 ------------------------- 103 104 Python provides two hooks to let you customize it: :mod:`sitecustomize` and 105 :mod:`usercustomize`. To see how it works, you need first to find the location 106 of your user site-packages directory. Start Python and run this code:: 107 108 >>> import site 109 >>> site.getusersitepackages() 110 '/home/user/.local/lib/python2.7/site-packages' 111 112 Now you can create a file named :file:`usercustomize.py` in that directory and 113 put anything you want in it. It will affect every invocation of Python, unless 114 it is started with the :option:`-s` option to disable the automatic import. 115 116 :mod:`sitecustomize` works in the same way, but is typically created by an 117 administrator of the computer in the global site-packages directory, and is 118 imported before :mod:`usercustomize`. See the documentation of the :mod:`site` 119 module for more details. 120 121 122 .. rubric:: Footnotes 123 124 .. [#] A problem with the GNU Readline package may prevent this. 125
