[issue22180] operator.setitem example no longer works in Python 3 due to lazy map
New submission from Michael Williamson:
The Python docs for the operator module include an example using map and
setitem to "Build a dictionary that maps the ordinals from 0 to 255 to their
character equivalents.":
d = {}
keys = range(256)
vals = map(chr, keys)
map(operator.setitem, [d]*len(keys), keys, vals)
Since map is lazy since Python 3, the dictionary d is never actually changed in
this example. I'm not entirely sure what the idiomatic way to fix the example
is since it strikes me as being fairly unidiomatic to begin with, but the
simplest would be to call list on the result of map to force evaluation (patch
attached).
--
assignee: docs@python
components: Documentation
files: doc-operator-example.patch
keywords: patch
messages: 225141
nosy: docs@python, mwilliamson
priority: normal
severity: normal
status: open
title: operator.setitem example no longer works in Python 3 due to lazy map
versions: Python 3.1, Python 3.2, Python 3.3, Python 3.4, Python 3.5
Added file: http://bugs.python.org/file36333/doc-operator-example.patch
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[issue22243] Documentation on try statement incorrectly implies target of except clause can be any assignable expression
New submission from Michael Williamson:
In the docs for the try statement [1], part of the grammar is:
try1_stmt ::= "try" ":" suite
("except" [expression ["as" target]] ":" suite)+
["else" ":" suite]
["finally" ":" suite]
The `target` rule allows any assignable expression (identifier, attributes,
etc.). However, CPython appears to only allow identifiers as a target. The
abstract grammar in the ast module [2] appears to confirm this.
[1] https://docs.python.org/3.4/reference/compound_stmts.html#the-try-statement
[2] https://docs.python.org/3.4/library/ast.html#abstract-grammar
--
assignee: docs@python
components: Documentation
messages: 225611
nosy: docs@python, mwilliamson
priority: normal
severity: normal
status: open
title: Documentation on try statement incorrectly implies target of except
clause can be any assignable expression
versions: Python 3.4, Python 3.5
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[issue22243] Documentation on try statement incorrectly implies target of except clause can be any assignable expression
Michael Williamson added the comment:
> Using 'expression' (or 'expr' in the ast doc) for what should be 'exceptions:
> identifier' or paranthesized tuple of identifiers;, is also too broad.
> However, that must be enforced in the compiler rather than the parser, and
> compiler restrictions are in the text, not the grammar.
I would expect any expression to be valid so long as it evaluates at runtime to
an exception type (or tuple of exception types), so the use of expression seems
correct to me. In other words, the following is valid Python (but would not be
allowed if I've understood your statement correctly):
def f():
try:
"".blah
except some_error():
print("caught")
def some_error():
return AttributeError
f()
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