Errata

The sentence "For example, x=x+y does not modify the object to which name x was
originally bound" is incorrect, I think. Suppose x and y belong to a user-defined
class in which __add__ has been defined. Suppose __add__(self, other)

changes some

attribute (say 'value') of self. Suppose we make the statements:

z=x

x = x+y

print z.value

The point of the discussion in the book is that x is reassigned, not changed in
place. However, the object originally bound to x will be changed in
place, and that change can be seen here in z.
The introduction of a custom __add__ is not so out of left field here, since
the book is contrasting the situation to when the object has a custom __iadd__.

AM: substitute /For example, x=x+y/For example, the assignment in x=x+y/ .

The sentence "For example, x=x+y does not modify the object to which name x was
originally bound" is incorrect, I think. Suppose x and y belong to a user-defined
class in which __add__ has been defined. Suppose __add__(self, other)

changes some

attribute (say 'value') of self. Suppose we make the statements:

z=x

x = x+y

print z.value

The point of the discussion in the book is that x is reassigned, not changed in
place. However, the object originally bound to x will be changed in
place, and that change can be seen here in z.
The introduction of a custom __add__ is not so out of left field here, since
the book is contrasting the situation to when the object has a custom __iadd__.

AM: substitute /For example, x=x+y/For example, the assignment in x=x+y/ .

For this code block to be illustrative of the distinction between legacy- and new-style resolution order and to be consonant with the phrase '...for the case of this kind of "diamond-shaped" inheritance graph' in the second paragraph on the following page class Base3, like Base2, should derive from Base1.

With Base3 not deriving from Base1 the code prints "Base1" even if it is modified to be new-style (by deriving Base1 from object).

Note from the Author or Editor:
change the 4th line of the code block from the current

class Base3:

to

class Base3(Base1):

Book says: "When __hash__ is absent, but __cmp__ or __eq__ is present, hash(x), and the use of x as a dictionary key, raise an exception."

This is confusing because in new-style classes, the __hash__ inherited from object doesn't throw an exception even if __cmp__ or __eq__ is defined and __hash__ is not overridden.

Note from the Author or Editor:
Add at the end of the 3rd paragraph (after "a dictionary key.") the following sentencse:

Note that `__hash__` "is present" even when it's not coded directly in the object's class but inherited from a base class. For example, a new-style class which subclasses `object` inherits a __hash__ which unconditionally calls `id`.

In the __getitem__ example, self.indices should be index.indices; also, one
parenthesis seems to be missing at the end.

Note from the Author or Editor:
change the penultimate line of code at the bottom of p. 100 which now reads

for x in xrange(*self.indices(len(self)))

to read


for x in xrange(*index.indices(len(self))))

i.e. change self to index and add one closed paren to the end for a total of 4 closed parentheses while it now has only 3.

In the __getitem__ example, self.indices should be index.indices; also, one
parenthesis seems to be missing at the end.

AM: reader's right on both accounts, s/self.indices/index.indices/ AND
add a ) at the end of that same line

In the __getitem__ example, self.indices should be index.indices; also, one
parenthesis seems to be missing at the end.

AM: reader's right on both accounts, s/self.indices/index.indices/ AND
add a ) at the end of that same line

The integer code returned for unicode is [0,65534], but shouldn't it
be 65535? But if it cannot return 65535, I would have appreciated knowing why it wouldn't.

AM: reader's right, s/65534/65535/

The integer code returned for unicode is [0,65534], but shouldn't it
be 65535? But if it cannot return 65535, I would have appreciated knowing why it wouldn't.

AM: reader's right, s/65534/65535/

result of reduce() is the product of a sequence of numbers, but it is getting bound to 'thesum'.

AM: reader's right, to reduce confusion s/thesum/theprod/

result of reduce() is the product of a sequence of numbers, but it is getting bound to 'thesum'.

AM: reader's right, to reduce confusion s/thesum/theprod/

>>> import collections, operator
>>> def sorted_histograms(seq):
d = collections.defaultdict(int)
for item in seq: d[item] += 1
print d
return sorted(d.iteritems, key=operator.itemgetter(1), reverse=True)

>>> a = [ "b", "c", "d", "b", "c", "c", "e", "d"]
>>> b = sorted_histograms(a)
defaultdict(<type 'int'>, {'c': 3, 'b': 2, 'e': 1, 'd': 2})

Traceback (most recent call last):
File "<pyshell#4>", line 1, in <module>
b = sorted_histograms(a)
File "<pyshell#2>", line 9, in sorted_histograms
return sorted(d.iteritems, key=operator.itemgetter(1), reverse=True)
TypeError: 'builtin_function_or_method' object is not iterable
>>> b

Traceback (most recent call last):
File "<pyshell#5>", line 1, in <module>
b
NameError: name 'b' is not defined

Note from the Author or Editor:
on p. 175, in the first code snippet, change the start of the code line that now reads

return sorted(d.iteritems, key=operator

to read instead

return sorted(d.iteritems(), key=operator

i.e. add an open and a closed paren just before the first comma (the rest of the line must remain unchanged).

>>> import collections, operator

>>> def sorted_histograms(seq):

d = collections.defaultdict(int)

for item in seq: d[item] += 1

print d

return sorted(d.iteritems, key=operator.itemgetter(1), reverse=True)

>>> a = [ "b", "c", "d", "b", "c", "c", "e", "d"]

>>> b = sorted_histograms(a)

defaultdict(<type 'int'>, {'c': 3, 'b': 2, 'e': 1, 'd': 2})

Traceback (most recent call last):

File "<pyshell#4>", line 1, in <module>

b = sorted_histograms(a)

File "<pyshell#2>", line 9, in sorted_histograms

return sorted(d.iteritems, key=operator.itemgetter(1), reverse=True)

TypeError: 'builtin_function_or_method' object is not iterable

>>> b

Traceback (most recent call last):

File "<pyshell#5>", line 1, in <module>

b

NameError: name 'b' is not defined

AM: reader's right, s/sorted(d.iteritems, /sorted(d.iteritems(), /

>>> import collections, operator

>>> def sorted_histograms(seq):

d = collections.defaultdict(int)

for item in seq: d[item] += 1

print d

return sorted(d.iteritems, key=operator.itemgetter(1), reverse=True)

>>> a = [ "b", "c", "d", "b", "c", "c", "e", "d"]

>>> b = sorted_histograms(a)

defaultdict(<type 'int'>, {'c': 3, 'b': 2, 'e': 1, 'd': 2})

Traceback (most recent call last):

File "<pyshell#4>", line 1, in <module>

b = sorted_histograms(a)

File "<pyshell#2>", line 9, in sorted_histograms

return sorted(d.iteritems, key=operator.itemgetter(1), reverse=True)

TypeError: 'builtin_function_or_method' object is not iterable

>>> b

Traceback (most recent call last):

File "<pyshell#5>", line 1, in <module>

b

NameError: name 'b' is not defined

AM: reader's right, s/sorted(d.iteritems, /sorted(d.iteritems(), /

Doesn't heappop run in O(log(len(alist))) time instead of O(len(alist))? If it was
O(len(alist)), then heapsort would be O(n^2).

Note from the Author or Editor:
p. 177 last line under heappop, change the text

runs in O(len(alist)) time

to

runs in O(log(len(alist))) time

Doesn't heappop run in O(log(len(alist))) time instead of

O(len(alist))? If it was

O(len(alist)), then heapsort would be O(n^2).

AM: reader's right, s/O(len(alist))/O(log(len(alist)))/

Doesn't heappop run in O(log(len(alist))) time instead of

O(len(alist))? If it was

O(len(alist)), then heapsort would be O(n^2).

AM: reader's right, s/O(len(alist))/O(log(len(alist)))/

Should refer to page 166, not 198.

Also index on page 691 should reference page 166 under repr (in addition to 198)

fmt parameter is missing in function prototype.

Note from the Author or Editor:
p. 307 at the end first line of `strftime`, change the existing

d.strftime()

to be instead

d.strftime(fmt)

fmt parameter is missing in function prototype.

AM: reader's right, s/d.strftime()/d.strftime(fmt)/

fmt parameter is missing in function prototype.

AM: reader's right, s/d.strftime()/d.strftime(fmt)/

fmt argument missing from prototype.

Note from the Author or Editor:
on p. 311 under `strftime` change d.strftime() to d.strftime(fmt)

fmt argument missing from prototype.

AM: reader's right, s/d.strftime()/d.strftime(fmt)/

fmt argument missing from prototype.

AM: reader's right, s/d.strftime()/d.strftime(fmt)/

The second timedelta() call in the "print repr(timedelta...)" examples should be
changed from
timedelta(minutes=0.5)
to
timedelta(hours=-1)

for the example output to be correct.

Note from the Author or Editor:
on p.312 in the example under `timedelta` change the *SECOND* occurrence (only! leave the first one unchanged!) from

minutes=0.5

to

hours=-1

the rest of the code before, around and after that change must remain unchanged.

The second timedelta() call in the "print repr(timedelta...)" examples should be

changed from

timedelta(minutes=0.5)

to

timedelta(hours=-1)

for the example output to be correct.

AM: reader's right, s/minutes=0.5/hours=-1/ in that second example.

The second timedelta() call in the "print repr(timedelta...)" examples should be

changed from

timedelta(minutes=0.5)

to

timedelta(hours=-1)

for the example output to be correct.

AM: reader's right, s/minutes=0.5/hours=-1/ in that second example.

I don't know how critical exception handling is to the content of your code samples. A lot of books state up-front that they've done a minimal job in this regard, but I didn't see such a disclaimer in this book. I would have marked this as a "Serious technical mistake" except for this fact. It certainly could be serious for anyone who naively uses this in production code.

You present the ExternalInterfacing, Serializer, and Worker classes in the book (and to a lesser degree in the errata). But note what happens if the thread run() method encounters an exception by calling self.externalCallable. I believe the ExternalInterfacing/Serializer/Worker thread will terminate, and the thread calling request()/apply(), which is blocking by calling q.get(), will deadlock (assuming it keeps running at all, as http://docs.python.org/lib/module-thread.html suggests for the earlier thread module).

Note that the Worker thread may terminate but since it posts results asynchronously, this doesn't necessarily cause an actual deadlock. I don't see this addressed in the errata so I wanted to mention it.

My suggestion is to catch exceptions in run(), return them in lieu of results, detect exceptions in request()/apply(), and raise them when they occur. Raising isn't really possible for the Worker, but the exception could at least be put into the result queue.

Note from the Author or Editor:
Add in the front matter of the book a disclaimer: "the example code in this book is intended to provide concise examples, and therefore often does not deal with possible errors and anomalies with the rock-solidity required in production code".

it uses both "Import Tkinter" and "from Tkinter import *".
The first is unnecessary and would be incorrect if the other was removed.

Note from the Author or Editor:
in p. 449 in the code example remove the first line which now reads

import Tkinter

The example in this section was how to quickly sort a list of strings based on the second word in each
string. The operator.itemgetter technique incorrectly sorts based on the second character in each string,
not the second word.

Maybe use something like:

L.sort(key=lambda x: x.split()[1])

Note from the Author or Editor:
p. 486, first code snippet, change both lines of code to read instead

def secondword(a): return a.split(1)
L.sort(key=secondword)

The example in this section was how to quickly sort a list of strings based on the second word in
each string. The operator.itemgetter technique incorrectly sorts based on the second character in
each string, not the second word.

Maybe use something like:

L.sort(key=lambda x: x.split()[1])

AM: reader's right that the code at the almost-bottom of p.485 is incorrect, but the right fix
is to change those two lines into the following two lines instead:

def secondword(s): return s.split()[1]

L.sort(key=secondword)

The example in this section was how to quickly sort a list of strings based on the second word in
each string. The operator.itemgetter technique incorrectly sorts based on the second character in
each string, not the second word.

Maybe use something like:

L.sort(key=lambda x: x.split()[1])

AM: reader's right that the code at the almost-bottom of p.485 is incorrect, but the right fix
is to change those two lines into the following two lines instead:

def secondword(s): return s.split()[1]

L.sort(key=secondword)

It talks about POP protocol, and should talk about NNTP protocol.

AM: reader's right, s/POP/NNTP/

It talks about POP protocol, and should talk about NNTP protocol.

AM: reader's right, s/POP/NNTP/

Example program produces error message:

"Traceback (most recent call last):

File "C:xmlrpctest.py", line 6, in <module>

results = proxy.meerkat.getItems({'search':'Python', 'num_items':7})

File "C:Python25Libxmlrpclib.py", line 1147, in __call__

return self.__send(self.__name, args)

File "C:Python25Libxmlrpclib.py", line 1437, in __request

verbose=self.__verbose

File "C:Python25Libxmlrpclib.py", line 1191, in request

headers

ProtocolError: <ProtocolError for

www.oreillynet.com/meerkat/xml-rpc/server.php: 301 Moved Permanently>"

AM: reader's right, Meerkat is no longer available and was shut down March 2, 2006. Delete example.

Example program produces error message:

"Traceback (most recent call last):

File "C:xmlrpctest.py", line 6, in <module>

results = proxy.meerkat.getItems({'search':'Python', 'num_items':7})

File "C:Python25Libxmlrpclib.py", line 1147, in __call__

return self.__send(self.__name, args)

File "C:Python25Libxmlrpclib.py", line 1437, in __request

verbose=self.__verbose

File "C:Python25Libxmlrpclib.py", line 1191, in request

headers

ProtocolError: <ProtocolError for

www.oreillynet.com/meerkat/xml-rpc/server.php: 301 Moved Permanently>"

AM: reader's right, Meerkat is no longer available and was shut down March 2, 2006. Delete example.

Using jythonc (jython version 2.2.1):
If you want to see a jython class from java you need to extend a parent java class. So

class APythonClass:
...
must be

class APythonClass(java.lang.object):
...

Jython 2.5rc2 doesn't use jythonc (http://www.jython.org/Project/jythonc.html).

Note from the Author or Editor:
The reader is correct: please change `class APythonClass:` to `class APythonClass(java.lang.object):`. The book does NOT cover versions 2.5 and later so the remark about 2.5rc2 may be omitted.