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annotate Doc/lib/libuser.tex @ 25838:8540887bcec6 2.2

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Backport of 2.183: Fix memory leak in add_subclass() found by NealN with valgrind.
author Guido van Rossum <guido@python.org>
date Fri, 18 Oct 2002 13:42:21 +0000
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children fd4cbbeace79
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1 \section{\module{user} ---
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2 User-specific configuration hook}
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3
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4 \declaremodule{standard}{user}
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5 \modulesynopsis{A standard way to reference user-specific modules.}
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6
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7
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8 \indexii{.pythonrc.py}{file}
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9 \indexiii{user}{configuration}{file}
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11 As a policy, Python doesn't run user-specified code on startup of
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12 Python programs. (Only interactive sessions execute the script
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13 specified in the \envvar{PYTHONSTARTUP} environment variable if it
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14 exists).
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16 However, some programs or sites may find it convenient to allow users
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17 to have a standard customization file, which gets run when a program
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18 requests it. This module implements such a mechanism. A program
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19 that wishes to use the mechanism must execute the statement
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20
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21 \begin{verbatim}
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22 import user
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23 \end{verbatim}
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24
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25 The \module{user} module looks for a file \file{.pythonrc.py} in the user's
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26 home directory and if it can be opened, executes it (using
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27 \function{execfile()}\bifuncindex{execfile}) in its own (the
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28 module \module{user}'s) global namespace. Errors during this phase
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29 are not caught; that's up to the program that imports the
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30 \module{user} module, if it wishes. The home directory is assumed to
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31 be named by the \envvar{HOME} environment variable; if this is not set,
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32 the current directory is used.
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34 The user's \file{.pythonrc.py} could conceivably test for
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35 \code{sys.version} if it wishes to do different things depending on
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36 the Python version.
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37
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38 A warning to users: be very conservative in what you place in your
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39 \file{.pythonrc.py} file. Since you don't know which programs will
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40 use it, changing the behavior of standard modules or functions is
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41 generally not a good idea.
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43 A suggestion for programmers who wish to use this mechanism: a simple
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44 way to let users specify options for your package is to have them
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45 define variables in their \file{.pythonrc.py} file that you test in
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46 your module. For example, a module \module{spam} that has a verbosity
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47 level can look for a variable \code{user.spam_verbose}, as follows:
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48
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49 \begin{verbatim}
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50 import user
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51 try:
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52 verbose = user.spam_verbose # user's verbosity preference
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53 except AttributeError:
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54 verbose = 0 # default verbosity
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55 \end{verbatim}
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57 Programs with extensive customization needs are better off reading a
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58 program-specific customization file.
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60 Programs with security or privacy concerns should \emph{not} import
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61 this module; a user can easily break into a program by placing
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62 arbitrary code in the \file{.pythonrc.py} file.
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64 Modules for general use should \emph{not} import this module; it may
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65 interfere with the operation of the importing program.
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66
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67 \begin{seealso}
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68 \seemodule{site}{Site-wide customization mechanism.}
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69 \end{seealso}