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