Tip: The fread and the fclose functions will be explained below. The file may be opened in one of the following modes: Modes Description r Open a file for read only. File pointer starts at the beginning of the file w Open a file for write only. Erases the contents of the file or creates a new file if it doesn't exist. File pointer starts at the beginning of the file a Open a file for write only.
The following examples show how to read text synchronously and asynchronously from a text file using.NET for desktop apps. In both examples, when you create the. PHP 5 File Open/Read/Close. Contains the name of the file to read from and the second parameter specifies the. For a complete reference of filesystem. Award-winning reading solution with thousands of leveled readers, lesson plans, worksheets and assessments to teach guided reading, reading proficiency and.
The existing data in file is preserved. File pointer starts at the end of the file. Creates a new file if the file doesn't exist x Creates a new file for write only. Returns FALSE and an error if file already exists r+ Open a file for read/write. File pointer starts at the beginning of the file w+ Open a file for read/write. Erases the contents of the file or creates a new file if it doesn't exist. File pointer starts at the beginning of the file a+ Open a file for read/write.
The existing data in file is preserved. File pointer starts at the end of the file.
Creates a new file if the file doesn't exist x+ Creates a new file for read/write. Returns FALSE and an error if file already exists.
Fancier Output Formatting So far we’ve encountered two ways of writing values: expression statements and the statement. (A third way is using the write method of file objects; the standard output file can be referenced as sys.stdout. See the Library Reference for more information on this.) Often you’ll want more control over the formatting of your output than simply printing space-separated values. There are two ways to format your output; the first way is to do all the string handling yourself; using string slicing and concatenation operations you can create any layout you can imagine. The string types have some methods that perform useful operations for padding strings to a given column width; these will be discussed shortly.
The second way is to use the method. The module contains a class which offers yet another way to substitute values into strings. One question remains, of course: how do you convert values to strings?
Luckily, Python has ways to convert any value to a string: pass it to the or functions. The function is meant to return representations of values which are fairly human-readable, while is meant to generate representations which can be read by the interpreter (or will force a if there is no equivalent syntax).
For objects which don’t have a particular representation for human consumption, will return the same value as. Many values, such as numbers or structures like lists and dictionaries, have the same representation using either function. Strings and floating point numbers, in particular, have two distinct representations. Some examples. s = 'Hello, world.' str ( s ) 'Hello, world.' repr ( s ) 'Hello, world.'
' str ( 1.0 / 7.0 ) '0.57' repr ( 1.0 / 7.0 ) '0.5714285' x = 10. 3.25 y = 200.
200 s = 'The value of x is ' + repr ( x ) + ', and y is ' + repr ( y ) + '.' print s The value of x is 32.5, and y is 40000. # The repr of a string adds string quotes and backslashes. Hello = 'hello, world n ' hellos = repr ( hello ) print hellos 'hello, world n' # The argument to repr may be any Python object. Repr (( x, y, ( 'spam', 'eggs' ))) '(32.5, 40000, ('spam', 'eggs'))' Here are two ways to write a table of squares and cubes. f = open ( 'workfile', 'w' ) print f The first argument is a string containing the filename. The second argument is another string containing a few characters describing the way in which the file will be used.
Mode can be 'r' when the file will only be read, 'w' for only writing (an existing file with the same name will be erased), and 'a' opens the file for appending; any data written to the file is automatically added to the end. 'r+' opens the file for both reading and writing. The mode argument is optional; 'r' will be assumed if it’s omitted.
On Windows, 'b' appended to the mode opens the file in binary mode, so there are also modes like 'rb', 'wb', and 'r+b'. Python on Windows makes a distinction between text and binary files; the end-of-line characters in text files are automatically altered slightly when data is read or written. This behind-the-scenes modification to file data is fine for ASCII text files, but it’ll corrupt binary data like that in JPEG or EXE files. Be very careful to use binary mode when reading and writing such files. On Unix, it doesn’t hurt to append a 'b' to the mode, so you can use it platform-independently for all binary files.
Methods of File Objects The rest of the examples in this section will assume that a file object called f has already been created. To read a file’s contents, call f.read(size), which reads some quantity of data and returns it as a string.
Size is an optional numeric argument. When size is omitted or negative, the entire contents of the file will be read and returned; it’s your problem if the file is twice as large as your machine’s memory. Otherwise, at most size bytes are read and returned. If the end of the file has been reached, f.read will return an empty string ( ').
value = ( 'the answer', 42 ) s = str ( value ) f. Write ( s ) f.tell returns an integer giving the file object’s current position in the file, measured in bytes from the beginning of the file. To change the file object’s position, use f.seek(offset, fromwhat). The position is computed from adding offset to a reference point; the reference point is selected by the fromwhat argument. A fromwhat value of 0 measures from the beginning of the file, 1 uses the current file position, and 2 uses the end of the file as the reference point.
Rns 310 maps. Alternatively you can plug your MP3 player into the AUX-in socket for music on the move. The split screen displays both map and additional useful information for extra clarity. And there's no need to stop the music while you're following your route - the Navigation data can be copied on to the SD card so that the CD player is kept free for playing your music.
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Fromwhat can be omitted and defaults to 0, using the beginning of the file as the reference point. Saving structured data with Strings can easily be written to and read from a file. Numbers take a bit more effort, since the read method only returns strings, which will have to be passed to a function like, which takes a string like '123' and returns its numeric value 123. When you want to save more complex data types like nested lists and dictionaries, parsing and serializing by hand becomes complicated. Rather than having users constantly writing and debugging code to save complicated data types to files, Python allows you to use the popular data interchange format called. The standard module called can take Python data hierarchies, and convert them to string representations; this process is called serializing.
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Reconstructing the data from the string representation is called deserializing. Between serializing and deserializing, the string representing the object may have been stored in a file or data, or sent over a network connection to some distant machine.