home
***
CD-ROM
|
disk
|
FTP
|
other
***
search
/
The Datafile PD-CD 5
/
DATAFILE_PDCD5.iso
/
utilities
/
p
/
python
/
pyhtmldoc
/
f
/
file_objec
next >
Wrap
Text File
|
1996-11-14
|
5KB
|
90 lines
<TITLE>File Objects -- Python library reference</TITLE>
Next: <A HREF="../i/internal_objects" TYPE="Next">Internal Objects</A>
Prev: <A HREF="../t/the_null_object" TYPE="Prev">The Null Object</A>
Up: <A HREF="../o/other_built-in_types" TYPE="Up">Other Built-in Types</A>
Top: <A HREF="../t/top" TYPE="Top">Top</A>
<H3>2.1.7.8. File Objects</H3>
File objects are implemented using C's <CODE>stdio</CODE> package and can be
created with the built-in function <CODE>open()</CODE> described under
Built-in Functions below. They are also returned by some other
built-in functions and methods, e.g. <CODE>posix.popen()</CODE> and
<CODE>posix.fdopen()</CODE> and the <CODE>makefile()</CODE> method of socket
objects.
When a file operation fails for an I/O-related reason, the exception
<CODE>IOError</CODE> is raised. This includes situations where the
operation is not defined for some reason, like <CODE>seek()</CODE> on a tty
device or writing a file opened for reading.
<P>
Files have the following methods:
<P>
<DL><DT><B>close</B> () -- Method on file<DD>
Close the file. A closed file cannot be read or written anymore.
</DL>
<DL><DT><B>flush</B> () -- Method on file<DD>
Flush the internal buffer, like <CODE>stdio</CODE>'s <CODE>fflush()</CODE>.
</DL>
<DL><DT><B>isatty</B> () -- Method on file<DD>
Return <CODE>1</CODE> if the file is connected to a tty(-like) device, else
<CODE>0</CODE>.
</DL>
<DL><DT><B>read</B> ([<VAR>size</VAR>]) -- Method on file<DD>
Read at most <VAR>size</VAR> bytes from the file (less if the read hits
EOF or no more data is immediately available on a pipe, tty or
similar device). If the <VAR>size</VAR> argument is negative or omitted,
read all data until EOF is reached. The bytes are returned as a string
object. An empty string is returned when EOF is encountered
immediately. (For certain files, like ttys, it makes sense to
continue reading after an EOF is hit.)
</DL>
<DL><DT><B>readline</B> ([<VAR>size</VAR>]) -- Method on file<DD>
Read one entire line from the file. A trailing newline character is
kept in the string<A NAME="footnoteref1" HREF="#footnotetext1">(1)</A>
(but may be absent when a file ends with an
incomplete line). If the <VAR>size</VAR> argument is present and
non-negative, it is a maximum byte count (including the trailing
newline) and an incomplete line may be returned.
An empty string is returned when EOF is hit
immediately. Note: unlike <CODE>stdio</CODE>'s <CODE>fgets()</CODE>, the returned
string contains null characters (<CODE>'\0'</CODE>) if they occurred in the
input.
</DL>
<DL><DT><B>readlines</B> () -- Method on file<DD>
Read until EOF using <CODE>readline()</CODE> and return a list containing
the lines thus read.
</DL>
<DL><DT><B>seek</B> (<VAR>offset</VAR>, <VAR>whence</VAR>) -- Method on file<DD>
Set the file's current position, like <CODE>stdio</CODE>'s <CODE>fseek()</CODE>.
The <VAR>whence</VAR> argument is optional and defaults to <CODE>0</CODE>
(absolute file positioning); other values are <CODE>1</CODE> (seek
relative to the current position) and <CODE>2</CODE> (seek relative to the
file's end). There is no return value.
</DL>
<DL><DT><B>tell</B> () -- Method on file<DD>
Return the file's current position, like <CODE>stdio</CODE>'s <CODE>ftell()</CODE>.
</DL>
<DL><DT><B>truncate</B> ([<VAR>size</VAR>]) -- Method on file<DD>
Truncate the file's size. If the optional size argument present, the
file is truncated to (at most) that size. The size defaults to the
current position. Availability of this function depends on the
operating system version (e.g., not all UNIX versions support this
operation).
</DL>
<DL><DT><B>write</B> (<VAR>str</VAR>) -- Method on file<DD>
Write a string to the file. There is no return value. Note: due to
buffering, the string may not actually show up in the file until
the <CODE>flush()</CODE> or <CODE>close()</CODE> method is called.
</DL>
<DL><DT><B>writelines</B> (<VAR>list</VAR>) -- Method on file<DD>
Write a list of strings to the file. There is no return value.
(The name is intended to match <CODE>readlines</CODE>; <CODE>writelines</CODE>
does not add line separators.)
</DL>
<H2>---------- Footnotes ----------</H2>
<A NAME="footnotetext1" HREF="#footnoteref1">(1)</A>
The advantage of leaving the newline on is that an empty string
can be returned to mean EOF without being ambiguous. Another
advantage is that (in cases where it might matter, e.g. if you
want to make an exact copy of a file while scanning its lines)
you can tell whether the last line of a file ended in a newline
or not (yes this happens!).<P>