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File Methods

The built-in file function creates a file object. The resulting object has a number of operations that change the state of the file, read or write data, or return information about the file. In the following descriptions, f is a file object, created by the file.

Read Methods. The following methods read from a file. As data is read, the file position is advanced from the beginning to the end of the file. The file must be opened with a mode that includes or implies 'r' for these methods to work.

f. read ( [size] ) → string

Read as many as size characters from file f . If size is negative or omitted, the rest of the file is read.

f. readline ( [size] ) → string

Read the next line or as many as size characters from file f ; an incomplete line can be read. If size is negative or omitted, the next complete line is read. If a complete line is read, it includes the trailing newline character, \n. If the file is at the end, f. readline returns a zero length string. If the file has a blank line, this will be a string of length 1 (the newline character).

f. readlines ( [hint] ) → list of strings

Read the next lines or as many lines from the next hint characters from file f . The value of hint may be rounded up to match an internal buffer size. If hint is negative or omitted, the rest of the file is read. All lines will include the trailing newline character, \n. If the file is at the end, f. readline2 returns a zero length list.

Write Methods. The following methods writing to a file. As data is written, the file position is advanced, possibly growing the file. If the file is opened for write, the position begins at the beginning of the file. If the file is opened for append, the position begins at the end of the file. If the file does not already exist, both writing and appending are equivalent. The file must be opened with a mode that include 'a' or 'w' for these methods to work.

f. flush

Flush all accumulated data from the internal buffers of file f to the OS file. Depending on your OS, this may also force all the data to be written to the device.

f. write ( string )

Write the given string to file f . Buffering may mean that the string does not appear on any console until a close or flush operation is used.

f. writelines ( list )

Write the list of strings to file f . Buffering may mean that the strings do not appear on any console until a close or flush operation is used.

f. truncate [size]

Truncate file f . If size is not given, the file is truncated at the current position. If size is given, the file will be truncated at size . If the file isn't as large as the given size , the results vary by operating system. This function is not available on all platforms.

Position Control Methods. The current position of a file can be examined and changed. Ordinary reads and writes will alter the position. These methods will report the position, and allow you to change the position that will be used for the next operation.

f. seek ( offset , [ whence ] )

Change the position from which file f will be processed. There are three values for whence which determine the direction of the move. If whence is zero (the default), move to the absolute position given by offset . f.seek(0) will rewind file f. If whence is one, move relative to the current position by offset bytes. If offset is negative, move backwards; otherwise move forward. If whence is two, move relative to the end of file. f.seek(0,2) will advance file f to the end, making it possible to append to the file.

f. tell → integer

Return the position from which file f will be processed. This is a partner to the seek method; any position returned by the tell method can be used as an argument to the seek method to restore the file to that position.

Other Methods. These are additional useful methods of a file object.

f. close

Close file f . The closed flag is set. Any further operations (except a redundant close) raise an IOError exception.

f. fileno → integer

Return the internal file descriptor (FD) used by the OS library when working with file f . A number of Python modules provide functions that use the OS libraries; the OS libraries need the FD.

f. isatty → boolean

Return True if file f is connected to the console or keyboard.

f. closed

This attribute is True if file f is closed.

f. mode

This attribute of file f is the mode argument to the file function that was used to create the file object.

f. name

This attribute of file f is the filename argument to the file function that was used to create the file object.


 
 
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