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authorBenjamin Peterson <benjamin@python.org>2013-02-10 14:29:59 (GMT)
committerBenjamin Peterson <benjamin@python.org>2013-02-10 14:29:59 (GMT)
commit1ef876cd28aa2f76edffb6e4d209c6a49b5705ef (patch)
treeeeb6cbf3329f73d4ddce50aef3c912b9e4aef400 /Doc
parent34a2a87d17ff1730946adf86d23a4737271e53b3 (diff)
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evaluate positional defaults before keyword-only defaults (closes #16967)
Diffstat (limited to 'Doc')
-rw-r--r--Doc/reference/compound_stmts.rst17
1 files changed, 9 insertions, 8 deletions
diff --git a/Doc/reference/compound_stmts.rst b/Doc/reference/compound_stmts.rst
index d0d0646..c25c767 100644
--- a/Doc/reference/compound_stmts.rst
+++ b/Doc/reference/compound_stmts.rst
@@ -493,14 +493,15 @@ case the parameter's default value is substituted. If a parameter has a default
value, all following parameters up until the "``*``" must also have a default
value --- this is a syntactic restriction that is not expressed by the grammar.
-**Default parameter values are evaluated when the function definition is
-executed.** This means that the expression is evaluated once, when the function
-is defined, and that the same "pre-computed" value is used for each call. This
-is especially important to understand when a default parameter is a mutable
-object, such as a list or a dictionary: if the function modifies the object
-(e.g. by appending an item to a list), the default value is in effect modified.
-This is generally not what was intended. A way around this is to use ``None``
-as the default, and explicitly test for it in the body of the function, e.g.::
+**Default parameter values are evaluated from left to right when the function
+definition is executed.** This means that the expression is evaluated once, when
+the function is defined, and that the same "pre-computed" value is used for each
+call. This is especially important to understand when a default parameter is a
+mutable object, such as a list or a dictionary: if the function modifies the
+object (e.g. by appending an item to a list), the default value is in effect
+modified. This is generally not what was intended. A way around this is to use
+``None`` as the default, and explicitly test for it in the body of the function,
+e.g.::
def whats_on_the_telly(penguin=None):
if penguin is None: