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Diffstat (limited to 'doc/user/environments.in')
| -rw-r--r-- | doc/user/environments.in | 88 |
1 files changed, 80 insertions, 8 deletions
diff --git a/doc/user/environments.in b/doc/user/environments.in index dfe98f2..9ce5568 100644 --- a/doc/user/environments.in +++ b/doc/user/environments.in @@ -672,11 +672,8 @@ environment, of directory names, suffixes, etc. <sconstruct> env = Environment() - dict = env.Dictionary() - keys = dict.keys() - keys.sort() - for key in keys: - print "construction variable = '%s', value = '%s'" % (key, dict[key]) + for item in sorted(env.Dictionary().items()): + print "construction variable = '%s', value = '%s'" % item </sconstruct> </section> @@ -775,6 +772,82 @@ environment, of directory names, suffixes, etc. </section> <section> + <title>Handling Problems With Value Expansion</title> + + <para> + + If a problem occurs when expanding a construction variable, + by default it is expanded to <literal>''</literal> + (a null string), and will not cause scons to fail. + + <scons_example name="missing1"> + <file name="SConstruct" printme="1"> + env = Environment() + print "value is:", env.subst( '->$MISSING<-' ) + </file> + </scons_example> + + <scons_output example="missing1"> + <scons_output_command>scons -Q</scons_output_command> + </scons_output> + + This default behaviour can be changed using the &AllowSubstExceptions; + function. + When a problem occurs with a variable expansion it generates + an exception, and the &AllowSubstExceptions; function controls + which of these exceptions are actually fatal and which are + allowed to occur safely. By default, &NameError; and &IndexError; + are the two exceptions that are allowed to occur: so instead of + causing scons to fail, these are caught, the variable expanded to + <literal>''</literal> + and scons execution continues. + To require that all construction variable names exist, and that + indexes out of range are not allowed, call &AllowSubstExceptions; + with no extra arguments. + </para> + + <scons_example name="missing2"> + <file name="SConstruct" printme="1"> + AllowSubstExceptions() + env = Environment() + print "value is:", env.subst( '->$MISSING<-' ) + </file> + </scons_example> + + <scons_output example="missing2"> + <scons_output_command>scons -Q</scons_output_command> + </scons_output> + + <para> + This can also be used to allow other exceptions that might occur, + most usefully with the <literal>${...}</literal> construction + variable syntax. For example, this would allow zero-division to + occur in a variable expansion in addition to the default exceptions + allowed + </para> + + <scons_example name="missing3"> + <file name="SConstruct" printme="1"> + AllowSubstExceptions(IndexError, NameError, ZeroDivisionError) + env = Environment() + print "value is:", env.subst( '->${1 / 0}<-' ) + </file> + </scons_example> + + <scons_output example="missing3"> + <scons_output_command>scons -Q</scons_output_command> + </scons_output> + <sconstruct> + </sconstruct> + + <para> + If &AllowSubstExceptions; is called multiple times, each call + completely overwrites the previous list of allowed exceptions. + </para> + + </section> + + <section> <title>Controlling the Default &ConsEnv;: the &DefaultEnvironment; Function</title> <para> @@ -1556,11 +1629,10 @@ environment, of directory names, suffixes, etc. #!/usr/bin/env python import os import sys - if len(sys.argv) > 1: + if len(sys.argv) > 1: keys = sys.argv[1:] else: - keys = os.environ.keys() - keys.sort() + keys = sorted(os.environ.keys()) for key in keys: print " " + key + "=" + os.environ[key] </file> |