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124 lines
4.5 KiB
ReStructuredText
124 lines
4.5 KiB
ReStructuredText
.. _tut-appendix:
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********
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Appendix
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********
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.. _tut-interac:
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Interactive Mode
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================
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.. _tut-error:
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Error Handling
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--------------
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When an error occurs, the interpreter prints an error message and a stack trace.
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In interactive mode, it then returns to the primary prompt; when input came from
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a file, it exits with a nonzero exit status after printing the stack trace.
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(Exceptions handled by an :keyword:`except` clause in a :keyword:`try` statement
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are not errors in this context.) Some errors are unconditionally fatal and
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cause an exit with a nonzero exit; this applies to internal inconsistencies and
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some cases of running out of memory. All error messages are written to the
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standard error stream; normal output from executed commands is written to
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standard output.
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Typing the interrupt character (usually :kbd:`Control-C` or :kbd:`Delete`) to the primary or
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secondary prompt cancels the input and returns to the primary prompt. [#]_
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Typing an interrupt while a command is executing raises the
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:exc:`KeyboardInterrupt` exception, which may be handled by a :keyword:`try`
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statement.
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.. _tut-scripts:
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Executable Python Scripts
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-------------------------
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On BSD'ish Unix systems, Python scripts can be made directly executable, like
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shell scripts, by putting the line ::
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#!/usr/bin/env python3.5
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(assuming that the interpreter is on the user's :envvar:`PATH`) at the beginning
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of the script and giving the file an executable mode. The ``#!`` must be the
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first two characters of the file. On some platforms, this first line must end
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with a Unix-style line ending (``'\n'``), not a Windows (``'\r\n'``) line
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ending. Note that the hash, or pound, character, ``'#'``, is used to start a
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comment in Python.
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The script can be given an executable mode, or permission, using the
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:program:`chmod` command.
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.. code-block:: bash
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$ chmod +x myscript.py
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On Windows systems, there is no notion of an "executable mode". The Python
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installer automatically associates ``.py`` files with ``python.exe`` so that
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a double-click on a Python file will run it as a script. The extension can
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also be ``.pyw``, in that case, the console window that normally appears is
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suppressed.
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.. _tut-startup:
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The Interactive Startup File
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----------------------------
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When you use Python interactively, it is frequently handy to have some standard
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commands executed every time the interpreter is started. You can do this by
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setting an environment variable named :envvar:`PYTHONSTARTUP` to the name of a
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file containing your start-up commands. This is similar to the :file:`.profile`
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feature of the Unix shells.
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This file is only read in interactive sessions, not when Python reads commands
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from a script, and not when :file:`/dev/tty` is given as the explicit source of
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commands (which otherwise behaves like an interactive session). It is executed
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in the same namespace where interactive commands are executed, so that objects
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that it defines or imports can be used without qualification in the interactive
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session. You can also change the prompts ``sys.ps1`` and ``sys.ps2`` in this
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file.
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If you want to read an additional start-up file from the current directory, you
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can program this in the global start-up file using code like ``if
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os.path.isfile('.pythonrc.py'): exec(open('.pythonrc.py').read())``.
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If you want to use the startup file in a script, you must do this explicitly
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in the script::
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import os
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filename = os.environ.get('PYTHONSTARTUP')
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if filename and os.path.isfile(filename):
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with open(filename) as fobj:
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startup_file = fobj.read()
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exec(startup_file)
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.. _tut-customize:
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The Customization Modules
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-------------------------
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Python provides two hooks to let you customize it: :mod:`sitecustomize` and
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:mod:`usercustomize`. To see how it works, you need first to find the location
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of your user site-packages directory. Start Python and run this code::
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>>> import site
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>>> site.getusersitepackages()
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'/home/user/.local/lib/python3.5/site-packages'
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Now you can create a file named :file:`usercustomize.py` in that directory and
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put anything you want in it. It will affect every invocation of Python, unless
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it is started with the :option:`-s` option to disable the automatic import.
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:mod:`sitecustomize` works in the same way, but is typically created by an
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administrator of the computer in the global site-packages directory, and is
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imported before :mod:`usercustomize`. See the documentation of the :mod:`site`
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module for more details.
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.. rubric:: Footnotes
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.. [#] A problem with the GNU Readline package may prevent this.
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