Name
open
Synopsis
open(filename
,mode
='rb',compresslevel
=9)
Like
GzipFile(
filename
,mode
,compresslevel
)
,
but filename
is mandatory and there is no
provision for passing an already opened
fileobj
.
Say that you have some function
f
(
x
)
that writes data to a text file object x
,
typically by calling
x
.write
and/or
x
.writelines
. Getting
f
to write data to a
gzip
-compressed text file instead is easy:
import gzip underlying_file = open('x.txt.gz', 'wb') compressing_wrapper = gzip.GzipFile(fileobj=underlying_file, mode='wt') f(compressing_wrapper) compressing_wrapper.close( ) underlying_file.close( )
This example opens the underlying binary file
x.txt.gz
and explicitly wraps it with
gzip.GzipFile
, and thus, at the end, we need to
close each object separately. This is necessary because we want to
use two different modes: the underlying file must be opened in binary
mode (any translation of line endings would produce an invalid
compressed file), but the compressing wrapper must be opened in text
mode because we want the implicit translation of
os.linesep
to \n
. Reading back
a compressed text file, for example to display it on standard output,
is similar:
import gzip, xreadlines underlying_file = open('x.txt.gz', 'rb') uncompressing_wrapper = gzip.GzipFile(fileobj= underlying_file, mode='rt') for line in xreadlines.xreadlines(uncompressing_wrapper): print line, uncompressing_wrapper.close( ) underlying_file.close( )
This example uses module xreadlines
, covered earlier in this chapter, because ...
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