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| author | Georg Brandl <georg@python.org> | 2008-09-21 07:09:51 (GMT) |
|---|---|---|
| committer | Georg Brandl <georg@python.org> | 2008-09-21 07:09:51 (GMT) |
| commit | 528cdb1281d5c3348c9dae5fead23dac2705907d (patch) | |
| tree | 685f468f080eff17d98eba978fffad8d09bbd5c5 /Doc/reference/expressions.rst | |
| parent | 8b6dc5cfab23cdb945fec7f0b2827b4a2530ecfc (diff) | |
| download | cpython-528cdb1281d5c3348c9dae5fead23dac2705907d.zip cpython-528cdb1281d5c3348c9dae5fead23dac2705907d.tar.gz cpython-528cdb1281d5c3348c9dae5fead23dac2705907d.tar.bz2 | |
#3917: don't allow {} as a set display.
Diffstat (limited to 'Doc/reference/expressions.rst')
| -rw-r--r-- | Doc/reference/expressions.rst | 17 |
1 files changed, 3 insertions, 14 deletions
diff --git a/Doc/reference/expressions.rst b/Doc/reference/expressions.rst index 7931b95..974c500 100644 --- a/Doc/reference/expressions.rst +++ b/Doc/reference/expressions.rst @@ -223,7 +223,7 @@ A set display is denoted by curly braces and distinguishable from dictionary displays by the lack of colons separating keys and values: .. productionlist:: - set_display: "{" [`expression_list` | `comprehension`] "}" + set_display: "{" (`expression_list` | `comprehension`) "}" A set display yields a new mutable set object, the contents being specified by either a sequence of expressions or a comprehension. When a comma-separated @@ -231,19 +231,8 @@ list of expressions is supplied, its elements are evaluated from left to right and added to the set object. When a comprehension is supplied, the set is constructed from the elements resulting from the comprehension. - -Variables used in the generator expression are evaluated lazily in a separate -scope when the :meth:`next` method is called for the generator object (in the -same fashion as for normal generators). However, the :keyword:`in` expression -of the leftmost :keyword:`for` clause is immediately evaluated in the current -scope so that an error produced by it can be seen before any other possible -error in the code that handles the generator expression. Subsequent -:keyword:`for` and :keyword:`if` clauses cannot be evaluated immediately since -they may depend on the previous :keyword:`for` loop. For example: -``(x*y for x in range(10) for y in bar(x))``. - -The parentheses can be omitted on calls with only one argument. See section -:ref:`calls` for the detail. +An empty set cannot be constructed with ``{}``; this literal constructs an empty +dictionary. .. _dict: |