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TheBufferedReader class provides input buffering to tie Reader stream. The BufferedWriter cless provides output buffe ring to the Writer stream. Input buffe ring consists of prefetching dete and caching it in a memory queue so that, for example, not every call to tie read() method equeOes to e reed operation on tie physical I O. Output buffering applies writes to a memory image that is periodically written out to a character stream. You want buffering support for input end output streams, especially large ones, to gain speed and efficiency. BufferedReader end BufferedWriter heve all of tie methods thet Reader end Writer heve, es well es the following _init_ (Writer_in) creates e BufferedWriter instance with the specified output _init_(Writer_in, iBufSize) same es ebove but specifies tie size of tie buffer
Three implementations of the writer object interface are provided as examples by this module. Most applications will need to derive new writer classes from the NullWriter class. NullWriter() A writer that only provides the interface definition no actions are taken on any methods. This should be the base class for all writers that do not need to inherit any implementation methods. AbstractWriter() A writer that can be used in debugging formatters, but not much else. Each method simply announces itself by printing its name and arguments on standard output. DumbWriter( file , maxcol 72 ) A simple writer class that writes output on the file object passed in as file or, if file is omitted, on standard output. The output is simply word wrapped to the number of columns specified by maxcol. This class is suitable for reflowing a sequence of paragraphs.
Interfaces to create writers are dependent on the specific writer class being instantiated. The interfaces described as follows are the required interfaces that all writers must support once initialized. Although most applications can use the AbstractFormatter class as a formatter, the writer must typically be provided by the application. new_alignment(align) Sets the alignment style. The align value can be any object, but by convention is a string or None, where None indicates that the writer's preferred alignment should be used. Conventional align values are new_margin (margin, level) Sets the margin level to the integer level and the logical tag to margin. Interpretation of the logical tag is at the writer's discretion the only restriction on the value of the logical tag is that it not be a false value for non-zero values of level. new_styles (styles) Sets additional styles. The styles value is a tuple of arbitrary values the value AS_IS should be ignored. The styles tuple can be...
BufferedInputStream and BufferedOutputStream provide tiie soivu kind of support to InputStream and OutputStream thet BufferedReader and BufferedWriter provide to Reader and Writer input and output buffering to their respective derivations. As I said before, input buffering entails prefetching data and caching it in memory so that read operations don't have to fetch the data off a slow device. Output buffering applies write operations to a memory image that's periodically written out to
Every now and then, you run into a situation where the writer of a function has decided that you should have n arguments to the function. If you are using a function to open a file, and the arguments are the name and the mode, this makes sense. If, on the other hand, you are writing a function to determine the average of a group of numbers, it really doesn't. Python provides a method for writing a function that accepts a variable number of arguments. For example, rather than having to do this
Creates a connection to a SQLite database. database is a string that specifies the name of the database file. It can also be a string memory , in which case an in-memory database is used (note that this kind of database only persists as long as the Python process remains running and would be lost on program exit).The timeout parameter specifies the amount of time to wait for an internal reader-writer lock to be released when other connections are updating the database. By default, timeout is 5 seconds. When SQL statements such as INSERT or UPDATE are used, a new transaction is automatically started if one wasn't already in effect.The isolation_level parameter is a string that provides an optional modifier to the underlying SQL BEGIN statement that is used to start this transaction. Possible values are (the default), DEFERRED , EXCLUSIVE , or IMMEDIATE .The meaning of these settings is related to the underlying database lock and is as follows
Thanks to many people in the Python community. First, thanks to Guido van Rossum for writing a great language, for being a great leader, and for being patient with me when I asked for advice on the book. There are so many rock stars in the Python community who crank out useful tools that I use everyday. They include Ian Bicking, Fernando Perez and Villi Vainio, Mike Bayer, Gustavo Niemeyer, etc. Thanks Thanks to the great book by David Beazely, and his fantastic tutorial at PyCon 2008 on Generators. Thanks to other writers about Python and systems administration as well. You can find links to their work here Thanks also to the Repoze crew Tres Seaver and Chris McDonough (http repoze.org index.html).
The following attributes are defined for formatter instance objects writer Interacts with the formatter. add_hor_rule(*args, **kw) Inserts a horizontal rule in the output. A hard break is inserted if data is in the current paragraph, but the logical paragraph is not broken. The arguments and keywords are passed on to the writer's add_flowing_data(data) Provides data that should be formatted with collapsed whitespaces. Whitespace from preceeding and successive calls to add_flowing_data() is considered as well when the whitespace collapse is performed. The data that is passed to this method is expected to be word wrapped by the output device. Note that any word wrapping still must be performed by the writer object because of the need to rely on device and font information. add_literal_data(data) Provides data that should be passed to the writer unchanged. Whitespace, including newline and tab characters, is considered legal in the value of data. add_label_data(format, counter) Inserts a...
AbstractFormatter(writer) class add flowing data(data) add hor rule(*args, **kw) add label data(format, counter) add line break() add literal data(data) end paragraph(blanklines) formatter objects 2nd writer CGI scripts AbstractFormatter(writer) AbstractWriter() DumbWritergfiler, maxcol 7211) formatter objects 2nd HTMLParser 2nd NullFormatter( writer1) NullWriter() sgmllib module 2nd 3rd 4th SGMLParser 2nd 3rd 4th 5th writer objects 2nd close() method 2nd collecting formatter 2nd 3rd 4th sgmllib.SGMLParser 2nd writer 2nd links SGMLParser class 2nd 3rd 4th 5th start tag() start tag(attributes) unknown charref(ref) unknown endtag(tag) unknown entity(ref) unknown starttag(tag, attributes) writer objects 2nd 3rd modules NullFormatter( writer ) class NullWriter() class objects formatter 2nd 3rd 4th 5th writer 2nd 3rd opening outputting links from HTML files to, CGI scripts writer attribute writer objects 2nd 3rd
NullFormatter( writer ) A formatter that does nothing. If writer is omitted, a NullWriter instance is created. No methods of the writer are called by NullFormatter instances. Implementations should inherit from this class if implementing a writer interface but don't need to inherit any implementation. AbstractFormatter(writer) The standard formatter. This implementation has demonstrated wide applicability to many writers, and can be used directly in most circumstances. It has been used to implement a full-featured WWW browser.
Tie two main class types in javaJo are text oriented (cfaracter strefmst and binary oriented (byte ytreams). Subclasses of the Reader end Writer classes are text oriented tiiose of the InputStream and OutputSt ream clayses are binary oriented. Jeve 1.1's binary date input streams are complemented by somewhet equivalent text input streams. The parents of these clesses are the ebstrect clesses Reader end Writer. Having en equivalent set of text-oriented character stream clesses allows the convecs-on of Uiilcode text. Readers and Writers, like streams, can be chained together. For example, you can buffer e FileReader by chaining it to e BufferedReader. (Buffering will be explained shortly.)
There ere more than thirty I O clesses, not including interfaces and abstract clesses. This seems like e lot, but if you understand how Reader,Writer,InputStream, and OutputStream work, you can easily understand tie rest. Reader end Writer subclesses deal with character streams, thet is, text. InputStream and OutputSt ream subclasses deal with binary streams. An easy way to remember this is, if you can read it, use Reader end Writer if you can't, use InputStream end OutputStream.
The parser, formatter, and writer are all instance objects, so you need to create the instances before they can act. The parser works on the contents of the file or Web page, so you have to open and read a file or Web page before the parser, formatter, and writer can act.
Also, it has always struck me that Python's file-processing interfaces are not restricted to real, physical files. In fact, most file tools work with any kind of object that exposes the same interface as a real file object. Thus, a file reader cares only about read methods, and a file writer cares only about write methods. As long as the target object implements the expected protocol, all goes well.
I am amazed at Alex's patience with questions (and I questioned a lot). His dedication to excellence is a co-author's dream. When presented with feedback, he consistently responded with appreciation and focus on making the book better. He's one of the least ego-istical writers I've ever met.
Writer(csvfile , dialect , **fmtparam ) Returns a writer object that can be used to create a CSV file. csvfile is any file-like object that supports a write() method. dialect has the same meaning as for reader() and is used to handle differences between various CSV encodings. fmt-params has the same meaning as for readers. However, one additional keyword argument is available A writer instance, w, supports the following methods w.writerow(row) w.writerows(rows) Writes multiple rows of data. rows must be a sequence of rows as passed to the writerow() method. Returns a writer object that operates like the ordinary writer but writes dictionaries into output rows. fieldnames specifies the order and names of attributes that will be written to the file. restval is the value that's written if the dictionary being written is missing one of the field names in fieldnames. extrasaction is a string that specifies what to do if a dictionary being written has keys not listed in fieldnames.The...
A carpenter cannot create works of art without his hammer, saw, and drill. An electrician is helpless without a circuit tester. A politician is hopeless without his script writer. What do all of these things have in common Simple they are all tools that are used for professionals to accomplish their jobs. The job of a Python programmer is to create, maintain, enhance, and debug Python applications. Like any other sort of profession, the Python programmer needs tools to accomplish his or her task. In this chapter, we are going to look at some of the tools that are already built into the Python distribution that will be used in your unrelenting pursuit of Python perfection.
With four arguments will always receive four arguments. How can these two statements both be true The answer lies in something called a default argument. A default argument is one that the writer of a function defines to have a default value if the user does not specify a value. For example, let's say that I wanted to print out the copyright date for my application. The copyright date is a string containing some boilerplate legal text and a year from which that copyright is valid. Now, it would make sense to have a default year that happened to be the current year, wouldn't it So, we could write a function like this
The formatter module is used for generic output formatting by the HTMLParser class of the htmllib module. This module supports two interface definitions, each with multiple implementations Formatter and Writer. Formatter objects transform an abstract flow of formatting events into specific output events on writer objects. Formatters manage several stack structures to allow various properties of a writer object to be changed and restored writers need not be able to handle relative changes nor any sort of change back operation. Specific writer properties which can be controlled via formatter objects are horizontal alignment, font, and left margin indentations. A mechanism is provided that supports providing arbitrary, non-exclusive style settings to a writer as well. Additional interfaces facilitate formatting events that are not reversible, such as paragraph separation. The writer interface is required by the formatter interface. Writer objects encapsulate device interfaces. Abstract...
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