Errata

[Oct-31-09] Page 38, list comprehensions: 3.X loop variable scope

This page states that names bound inside a list comprehension are created in the scope containing the comprehension. True, but as clearly stated ahead on page 40, 3.X changes this to work like generator expressions, such that the loop variables are not accessible outside list comprehensions either.

To clarify, at the very end of the 2nd paragraph under "List comprehension expressions", change "where the comprehension resides." to "where the comprehension resides in 2.X (but local to the expression in 3.X).".

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[Nov-06-09] Page 43, adict.fromkeys() usually called on dict itself

This isn't a bug because fromkeys() may be called both on an actual dict instance ({}.fromkeys('abc')) or on the type name dict itself (dict.fromkeys('abc')), but the latter form is the far more typical usage.

To clarify, in the list term near mid page that reads "adict.fromkeys(seq [, value])", change "adict" to "dict". Also, at the end of this list entry's description, add the following text in parenthesis: "...set to value (callable on instance or type name).".

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[Oct-28-09] Page 46, infile.read() end-lines: default only

This section states that text mode files translate line-ends to '\n'. This is true, but only by default in Python 3.X; see the open() call on page 113 for its "newline" argument that can modify this.

To clarify, under infile.read(), change "line ends are translated to '\n'." to "line ends are translated to '\n' by default.".

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[Oct-28-09] Page 47, outfile.write() end-lines: default only

This section states that text mode files translate '\n' to the platform's line-end separator. This is true, but only by default in Python 3.X; see the open() call on page 113 for its "newline" argument that can modify this.

To clarify, under outfile.write(), change "line-end marker sequence." to "line-end marker sequence by default.".

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Nov-06-09] Page 48, additional file attributes

[No reprint fix required -- clarification only]

This page lists 3 common file object data attributes: closed, mode, and name. It's not intended to be complete, and there are many additional file attributes, the set of which varies widely between Python 2.X and 3.X. For the fiull story, consult Python manuals or run a dir(F) call on any open file object F.

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Nov-14-09] Page 64 and 73, add "[decoration]" to def and class syntax formats

The book covers function and class decorators on pages 67 and 74. Because they are tied to def and class statements syntactically, though, and because it looks like we have the room, I want to make this more explicit by adding a line that reads "[decoration]" just before the "def name..." format listing on page 64, and just before the "class name..." format listing on page 73.

In other words, these two code format layouts on these pages should look like (note that the indentation whitespace will be stripped in this code by this site -- please consult the original of this posting on my websit listed below for a more accurate description):

The def Statement

[decoration]
def name([arg,... arg=value,... *arg, **arg]):
suite

The class Statement

[decoration]
class name [ ( super [, super]* [, metaclass=M] ) ]:
suite

The two added lines should be fixed-with font, and their "decoration" should be italics/replaceable.

This is all fairly obvious in the decorator descriptions that follow these, and the syntax formats are not intended to be complete (they also don't include 3.X keyword-only arguments and function annotations, which are similarly described a few pages ahead). Still, given that decorators work in both 2.6 and 3.X and are used widely today, it would nice to include them in the syntax formats.

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[Nov-13-09] Page 74, bullet 4, describes instance method default only

Strictly speaking, this bullet describes the instance method model, which is the normal case for methods in a class (self recieves the instance). Keep in mind, though, that this is just the default; Python also has static methods (which receive no instance) and class methods (which receive a class in self). Moreover, Python 3.X class methods may be called as simple functions through a class with no instance at all, and need be declared static only if they are called through an instance.

This is not an errata, because the description is correct for the normal case, and this brief summary isn't intended to be a complete coverage of all method variants. The built-in functions section covers staticmethod() and classmethod(), and the book Learning Python presents the full story on all method types.

To clarify slightly, though, at the end of the 4th bullet on this page, add this: "The staticmethod() and classmethod() built-ins support additional kinds of methods, and Python 3.X methods may be treated as simple functions when called through a class." In this, "staticmethod()" and "classmethod()" are literals in fixed-width font. If this does not fit, delete the ", etc." at the end of bullet 2 to free up a line.

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[Oct-28-09] Page 111, 3.X open(), add link to 2.X version

Page 111 begins documenting the 3.X open() call. Although it's implied by the book's contents, it would nice to note the location of the corresponding 2.X open() description, given the prevalence of this call. At the start of the first paragraph under open(...), add "See also Python 2.X open() on page 123."

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(Correction added for inclusion in reprints from
http://www.rmi.net/~lutz/pyref4e-updates.html)
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[Jul-8-10] Page 148, os.listdir: pass bytes to suppress Unicode filename decode

At the very end of the listdir description (paragraph 1 on this page), if we have space, add the sentence: "In 3.X, passed and returns bytes instead of str to suppress Unicode filename decoding per platform default (also for glob, os.walk)."

This is a crucial point, as it's required to avoid exceptions for any undecodable filenames in 3.X. If we don't have space to add anything here, this note is clarification only; it's described in depth in Programming Python 4th Edition.

The "random" module is commonly used but is not listed in the commonly used library modules section.

Note from the Author or Editor:
Thanks for the suggestion, but this short reference cannot cover all interesting Python modules and retain its physical size. This module will, however, be added to a list of potential additions (along with timeit and others) for a later edition, if one ever materializes. Also changed this post's type to "question/clarification", from "minor technical mistake" (it's hardly the latter).

[Nov-06-09] Index, page 192, link to "def" at "functions"

In the index at "functions, 64", add "(see also def statements)". As is, most function details are indexed under "def", not "functions", but "functions" is the first place most readers will probably look.

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