Write datetime.strptime() item; show use of @contextmanager in defining __context__ methods; minor edits; add two names
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@ -145,7 +145,7 @@ around your conditional expressions, you won't run into this case.
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\begin{seealso}
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\seepep{308}{Conditional Expressions}{PEP written by
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Guido van Rossum and Raymond D. Hettinger; implemented by Thomas
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Guido van~Rossum and Raymond D. Hettinger; implemented by Thomas
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Wouters.}
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\end{seealso}
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@ -549,7 +549,7 @@ chance to run. The syntactic restriction that you couldn't mix
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therefore been removed. This seems like a minor bit of language
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trivia, but using generators and \code{try...finally} is actually
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necessary in order to implement the \keyword{with} statement
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described by PEP 343. We'll look at this new statement in the following
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described by PEP 343. I'll look at this new statement in the following
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section.
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Another even more esoteric effect of this change: previously, the
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@ -560,7 +560,7 @@ once the generator has been exhausted.
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\begin{seealso}
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\seepep{342}{Coroutines via Enhanced Generators}{PEP written by
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Guido van Rossum and Phillip J. Eby;
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Guido van~Rossum and Phillip J. Eby;
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implemented by Phillip J. Eby. Includes examples of
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some fancier uses of generators as coroutines.}
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@ -581,10 +581,10 @@ The \keyword{with} statement allows a clearer version of code that
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uses \code{try...finally} blocks to ensure that clean-up code is
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executed.
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First, I'll discuss the statement as it will commonly be used, and
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then a subsection will examine the implementation details and how to
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write objects (called ``context managers'') that can be used with this
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statement.
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In this section, I'll discuss the statement as it will commonly be
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used. In the next section, I'll examine the implementation details
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and show how to write objects called ``context managers'' and
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``contexts'' for use with this statement.
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The \keyword{with} statement is a new control-flow structure whose
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basic structure is:
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@ -830,10 +830,29 @@ with db_transaction(db) as cursor:
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...
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\end{verbatim}
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You can also use this decorator to write the \method{__context__()} method
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for a class without creating a new class for the context:
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\begin{verbatim}
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class DatabaseConnection:
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@contextmanager
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def __context__ (self):
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cursor = self.cursor()
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try:
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yield cursor
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except:
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self.rollback()
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raise
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else:
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self.commit()
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\end{verbatim}
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There's a \function{nested(\var{mgr1}, \var{mgr2}, ...)} manager that
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combines a number of context managers so you don't need to write
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nested \keyword{with} statements. This example
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both uses a database transaction and also acquires a thread lock:
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nested \keyword{with} statements. This example statement does two
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things, starting a database transaction and acquiring a thread lock:
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\begin{verbatim}
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lock = threading.Lock()
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@ -853,8 +872,8 @@ with closing(open('/tmp/file', 'r')) as f:
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\begin{seealso}
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\seepep{343}{The ``with'' statement}{PEP written by Guido van Rossum
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and Nick Coghlan; implemented by Mike Bland, Guido van Rossum, and
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\seepep{343}{The ``with'' statement}{PEP written by Guido van~Rossum
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and Nick Coghlan; implemented by Mike Bland, Guido van~Rossum, and
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Neal Norwitz. The PEP shows the code generated for a \keyword{with}
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statement, which can be helpful in learning how context managers
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work.}
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@ -926,7 +945,7 @@ in a few releases.
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\begin{seealso}
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\seepep{352}{Required Superclass for Exceptions}{PEP written by
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Brett Cannon and Guido van Rossum; implemented by Brett Cannon.}
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Brett Cannon and Guido van~Rossum; implemented by Brett Cannon.}
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\end{seealso}
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@ -1174,9 +1193,6 @@ the SVN logs for all the details.
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% the cPickle module no longer accepts the deprecated None option in the
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% args tuple returned by __reduce__().
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% XXX datetime.datetime() now has a strptime class method which can be used to
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% create datetime object using a string and format.
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% XXX fileinput: opening hook used to control how files are opened.
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% .input() now has a mode parameter
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% now has a fileno() function
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@ -1250,6 +1266,19 @@ read from the source; records can span multiple physical lines, so
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\member{line_num} is not the same as the number of records read.
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(Contributed by Skip Montanaro and Andrew McNamara.)
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\item The \class{datetime} class in the \module{datetime}
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module now has a \method{strptime(\var{string}, \var{format})}
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method for parsing date strings, contributed by Josh Spoerri.
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It uses the same format characters as \function{time.strptime()} and
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\function{time.strftime()}:
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\begin{verbatim}
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from datetime import datetime
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ts = datetime.strptime('10:13:15 2006-03-07',
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'%H:%M:%S %Y-%m-%d')
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\end{verbatim}
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\item In the \module{gc} module, the new \function{get_count()} function
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returns a 3-tuple containing the current collection counts for the
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three GC generations. This is accounting information for the garbage
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@ -1943,6 +1972,7 @@ freed with the corresponding family's \cfunction{*_Free()} function.
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The author would like to thank the following people for offering
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suggestions, corrections and assistance with various drafts of this
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article: Martin von~L\"owis, Mike Rovner, Thomas Wouters.
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article: Phillip J. Eby, Kent Johnson, Martin von~L\"owis, Mike
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Rovner, Thomas Wouters.
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\end{document}
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