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Expand a bit on genexp scopes.

This commit is contained in:
Georg Brandl 2008-03-03 21:31:50 +00:00
parent d2f7680b8f
commit 8e67ef52db
1 changed files with 9 additions and 8 deletions
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Doc/reference/expressions.rst
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@ -230,14 +230,15 @@ generator are those that would be produced by considering each of the
evaluating the expression to yield a value that is reached the innermost block
for each iteration.
Variables used in the generator expression are evaluated lazily when the
:meth:`next` method is called for generator object (in the same fashion as
normal generators). However, the leftmost :keyword:`for` clause is immediately
evaluated so that error produced by it can be seen before any other possible
error in the code that handles the generator expression. Subsequent
:keyword:`for` 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))``.
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.