Errata

1) A blank space should precede the backslash in line 1.
2) This code doesn't seem to work unless line 2 starts at column 1, thus breaking indentation rules.

class TestText:
def test_multiple_lines(self):
big = "This is a long string
that spans two lines."
assert big == 'This is a long string that spans two lines.',
'Error for %s' % big

(test_text.TestText.test_multiple_lines ... ok)

BOOK: Python Cookbook by Alex Martelli; Anna Martelli Ravenscroft; David
Ascher
PUBLISHER: O'Reilly Media, Inc.
DATE OF PUBLICATION: March 18, 2005
Chapter 12. Processing XML
Section: Converting an XML Document into a tree of Python Objects
12.6.2 Solution

[Code... snippet]
def EndElement(self, name):
'Expat end element event handler'
self.nodeStack[-1].pop( )

The code above attempts execute the method pop on an Element object
contained in the nodeStack(list). However, there is no method pop defined
in the Element Class. I believe that it was the authors intention to write.

[Code... snippet]
def EndElement(self, name):
'Expat end element event handler'
self.nodeStack.pop( )

Which pops an element of the stack.

The example code about "compress" is shown to return a value that is different from the value obtained in practice.

From the book:

>>> list(compress(addresses, more5))
['5800 E 58TH', '4801 N BROADWAY', '1039 W GRANVILLE']

Actual result:

['5800 E 58TH', '1060 W ADDISON', '4801 N BROADWAY']

The code reads output.close() instead of output_file.close() and input.close() instead of input_file.close()

This results in the following error:
Traceback (most recent call last):
File "./replace", line 18, in <module>
output.close()
NameError: name 'output' is not defined

The last argument passed in to all_files() - yield_folders
doesn't do what its name implies.

The function returns the same output whether yield_folders is set to True or False.

The Directory Walker solution in the first edition of this book has a similar problem.

One solution:
remove these lines

if return_folders:
files.extend(subdirs)

and change this:
if fnmatch.fnmatch(name, pattern):
yield os.path.join(path, name)
break

to this:

if fnmatch.fnmatch(name, pattern):
if return_folders:
yield path, os.path.join(path, name)
else:
yield os.path.join(path, name)
break

I may have found something worth correcting and would like to share it with you. The apparent mistake can be found on page 96 in the comments in the code (Solution) of recipe 2.22 "Computing the relative path from one directory to another".

The comments on the code refer to "unique tails", this statement isn't always true. There are several ways in which the resulting tails would not be unique. This is an example to illustrate this:
>>> li1 = [1,2,3,4]
>>> li2 = [1,2,4,5]
>>> li3 = [1,2,4,5]
>>> common_prefix(li1, li2, li3)
([1, 2], [[3, 4], [4, 5], [4, 5]])

As you may see the second element in the tuple - the list containing the 'tails' - contains the 'tail' [4, 5] twice. I'm using numbers here for the sake of the example but for paths the same is off course true.

By the time this statement is executed we had already determined that there must be either 1 or 2 command line args passed in otherwise the script would have exited. However now we are checking whether numargs < 3 where numargs = len(sys.argv) - 1. This condition will always be true i.e. if len(sys.argv) = 3 then numargs = 2 and numargs will always be less than 3, therefore the else clause will never be executed AFAICT.

The source code listing has

return tokenDict[word]()

Running the code example throws the error:
SyntaxError: 'return' outside function

which is right, this code is not within a function.

Delete 'return' and the code example runs.

def __new__(cls, *args, **kwargs):
if '_inst' not in vars(cls):
cls._inst = type.__new__(cls, *args, **kwargs)

return cls._inst


should be (type changed to super...):


def __new__(cls, *args, **kwargs):
if '_inst' not in vars(cls):
cls._inst = super(Null, cls).__new__(cls, *args, **kwargs)

return cls._inst

After inserting values into the db, the connection.commit() is missing. Without it the data won't get into the database.

wr.SetValueEx(..., REG_SZ,..) => wr.REG_SZ

after both finally:
CloseKey(...) => wr.CloseKey(...)

for k, v in kw:
should be
for k, v in kw.iteritems():

I'm a newbie, so maybe I'm missing something, but I think there is a slight mistake in a recipe in the Python Cookbook (2nd Ed., 2005). I'm also submitting this on the O'Reilly site.

12.5 Converting an XML Document into a Tree of Python Objects (p.471-472)

Cookbook code:

class Xml2Obj:
EndElement():
...
self.nodeStack[-1].pop()

Suggested code:
self.nodeStack.pop(-1)

With that change, the recipe works (python version 2.5) -- without it, it bombs.

nodeStack is a list of Element objects. Element objects gather up the tagnames, attributes, and a list of children elements of Element nodes in an XML object. They aren't lists and don't have a pop() method. But the code pulls the last Element off the nodeStack, and calls pop() on that Element.

The suggested code call pop() on nodeStack, which is a list, pulling off the last of its elements.

1 def cross_loop( *sequences ) :
2 # from _Python Cookbook_, 2e pg 712
3 if sequences :
4 for x in sequences[0] :
5 for y in cross_loop( *sequences[1:] ) :
6 yield (x,) + y
7 else :
8 yield ()

I added the "*" to the cross_loop() call in line 5. Otherwise, I think, the bare
sequences[1:] would pass the slice into the recursive call to cross_loop(). The inner
calls' sequences would then be a length 1 array containing the tuples from the slice.

I'm not too sure I wasn't simply calling the function incorrectly.

def cross_product( self ) :
return cross_loop( self.y_radius_range,
self.cbcr_radius_range,
self.scale_10_range,
self.scale_15_range,
self.scale_20_range,
self.output_scale_range )

All those "_range" members are tuples of integers.

An eventual simplification was:
def cross_product( self ) :
sequences = []
for f in self.iterable_field_names :
sequences.append( getattr( self, f+"_range" ) )
return cross_loop( *sequences )

Both of those functions worked when I added the "*" to the front of the sequences[1:]
slice in the recursive call.