mirror of https://github.com/python/cpython
61 lines
2.4 KiB
TeX
61 lines
2.4 KiB
TeX
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\section{Standard Module \sectcode{user}}
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\label{module-user}
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\stmodindex{user}
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\kwindex{.pythonrc.py}
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As a policy, Python doesn't run user-specified code on startup of
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Python programs. (Only interactive sessions execute the script
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specified in the \code{PYTHONPATH} environment variable if it exists).
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However, some programs or sites may find it convenient to allow users
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to have a standard customization file, which gets run when a program
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requests it. This module implements such a mechanism. A program
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that wishes to use the mechanism must execute the statement
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\bcode\begin{verbatim}
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import user
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\end{verbatim}\ecode
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The user module looks for a file \file{.pythonrc.py} in the user's
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home directory and if it can be opened, exececutes it (using
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\code{execfile()}) in its own (i.e. the module \code{user}'s) global
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namespace. Errors during this phase are not caught; that's up to the
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program that imports the user module, if it wishes. The home
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directory is assumed to be named by the \code{HOME} environment
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variable; if this is not set, the current directory is used.
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The user's \file{.pythonrc.py} could conceivably test for
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\code{sys.version} if it wishes to do different things depending on
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the Python version.
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A warning to users: be very conservative in what you place in your
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\file{.pythonrc.py} file. Since you don't know which programs will
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use it, changing the behavior of standard modules or functions is
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generally not a good idea.
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A suggestion for programmers who wish to use this mechanism: a simple
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way to let users specify options for your package is to have them
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define variables in their \var{.pythonrc.py} file that you test in
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your module. For example, a module \code{spam} that has a verbosity
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level can look for a variable \code{user.spam_verbose}, as follows:
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\bcode\begin{verbatim}
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import user
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try:
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verbose = user.spam_verbose # user's verbosity preference
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except AttributeError:
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verbose = 0 # default verbosity
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\end{verbatim}\ecode
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Programs with extensive customization needs are better off reading a
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program-specific customization file.
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Programs with security or privacy concerns should \emph{not} import
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this module; a user can easily break into a a program by placing
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arbitrary code in the \file{.pythonrc.py} file.
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Modules for general use should \emph{not} import this module; it may
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interfere with the operation of the importing program.
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For a site-wide customization mechanism, see module \code{site}.
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