Doc/lib/libuser.tex

   1 \section{\module{user} ---
   2          User-specific configuration hook}
   3
   4 \declaremodule{standard}{user}
   5 \modulesynopsis{A standard way to reference user-specific modules.}
   6
   7
   8 \indexii{.pythonrc.py}{file}
   9 \indexiii{user}{configuration}{file}
  10
  11 As a policy, Python doesn't run user-specified code on startup of
  12 Python programs.  (Only interactive sessions execute the script
  13 specified in the \envvar{PYTHONSTARTUP} environment variable if it
  14 exists).
  15
  16 However, some programs or sites may find it convenient to allow users
  17 to have a standard customization file, which gets run when a program
  18 requests it.  This module implements such a mechanism.  A program
  19 that wishes to use the mechanism must execute the statement
  20
  21 \begin{verbatim}
  22 import user
  23 \end{verbatim}
  24
  25 The \module{user} module looks for a file \file{.pythonrc.py} in the user's
  26 home directory and if it can be opened, executes it (using
  27 \function{execfile()}\bifuncindex{execfile}) in its own (the
  28 module \module{user}'s) global namespace.  Errors during this phase
  29 are not caught; that's up to the program that imports the
  30 \module{user} module, if it wishes.  The home directory is assumed to
  31 be named by the \envvar{HOME} environment variable; if this is not set,
  32 the current directory is used.
  33
  34 The user's \file{.pythonrc.py} could conceivably test for
  35 \code{sys.version} if it wishes to do different things depending on
  36 the Python version.
  37
  38 A warning to users: be very conservative in what you place in your
  39 \file{.pythonrc.py} file.  Since you don't know which programs will
  40 use it, changing the behavior of standard modules or functions is
  41 generally not a good idea.
  42
  43 A suggestion for programmers who wish to use this mechanism: a simple
  44 way to let users specify options for your package is to have them
  45 define variables in their \file{.pythonrc.py} file that you test in
  46 your module.  For example, a module \module{spam} that has a verbosity
  47 level can look for a variable \code{user.spam_verbose}, as follows:
  48
  49 \begin{verbatim}
  50 import user
  51
  52 verbose = bool(getattr(user, "spam_verbose", 0))
  53 \end{verbatim}
  54
  55 (The three-argument form of \function{getattr()} is used in case
  56 the user has not defined \code{spam_verbose} in their
  57 \file{.pythonrc.py} file.)
  58
  59 Programs with extensive customization needs are better off reading a
  60 program-specific customization file.
  61
  62 Programs with security or privacy concerns should \emph{not} import
  63 this module; a user can easily break into a program by placing
  64 arbitrary code in the \file{.pythonrc.py} file.
  65
  66 Modules for general use should \emph{not} import this module; it may
  67 interfere with the operation of the importing program.
  68
  69 \begin{seealso}
  70   \seemodule{site}{Site-wide customization mechanism.}
  71 \end{seealso}