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bpo-43755: Update docs to reflect that lambda is not allowed in comp_if since 3.9 #25231

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pablogsal merged 1 commit into from
Apr 6, 2021
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bpo-43755: Update docs to reflect that lambda is not allowed in comp_if since 3.9 #25231

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4 changes: 1 addition & 3 deletions Doc/reference/expressions.rst
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Expand Up @@ -185,7 +185,7 @@ Common syntax elements for comprehensions are:
comprehension: `assignment_expression` `comp_for`
comp_for: ["async"] "for" `target_list` "in" `or_test` [`comp_iter`]
comp_iter: `comp_for` | `comp_if`
comp_if: "if" `expression_nocond` [`comp_iter`]
comp_if: "if" `or_test` [`comp_iter`]

The comprehension consists of a single expression followed by at least one
:keyword:`!for` clause and zero or more :keyword:`!for` or :keyword:`!if` clauses.
Expand Down Expand Up @@ -1707,7 +1707,6 @@ Conditional expressions
.. productionlist:: python-grammar
conditional_expression: `or_test` ["if" `or_test` "else" `expression`]
expression: `conditional_expression` | `lambda_expr`
expression_nocond: `or_test` | `lambda_expr_nocond`

Conditional expressions (sometimes called a "ternary operator") have the lowest
priority of all Python operations.
Expand All @@ -1733,7 +1732,6 @@ Lambdas

.. productionlist:: python-grammar
lambda_expr: "lambda" [`parameter_list`] ":" `expression`
lambda_expr_nocond: "lambda" [`parameter_list`] ":" `expression_nocond`

Lambda expressions (sometimes called lambda forms) are used to create anonymous
functions. The expression ``lambda parameters: expression`` yields a function
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4 changes: 4 additions & 0 deletions Doc/whatsnew/3.9.rst
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Expand Up @@ -267,6 +267,10 @@ Other Language Changes
:func:`~operator.countOf` of the :mod:`operator` module.
(Contributed by Serhiy Storchaka in :issue:`40824`.)

* Unparenthesized lambda expressions can no longer be the expression part in an
``if`` clause in comprehensions and generator expressions. See :issue:`41848`
and :issue:`43755` for details.


New Modules
===========
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3 changes: 3 additions & 0 deletions Misc/NEWS.d/next/Documentation/2021-04-06-14-55-45.bpo-43755.1m0fGq.rst
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@@ -0,0 +1,3 @@
Update documentation to reflect that unparenthesized lambda expressions can
no longer be the expression part in an ``if`` clause in comprehensions and
generator expressions since Python 3.9.