*-------[ First off { entry level, easy access }*
Opening and reading files with a one-liner in python is a cool trick to
know, i.e.
*x = open( os.path.join( “this” , “that” ) ).readlines()*
But can lead to a scenario where one forgets to close the file handle
again, and for each time the code runs there will be a lingering file still
open in memory causing various things to get offset.
This would be things like:
- · Marginal memory prints not being available again until at
reboot
- · Lingering .nfs* files on network servers.
- · General trash borderlining on a memory leak definition.
*x.close()*
With the line above ensures the file is closed again after use.
*-------[ Secondly { intermidiate, efficient }*
The mess assosciated with this is one of the primary reason why the “
*with*” statement was added to Python, the general file object was upgraded
to inlude __enter__ and __exit__ methods so when you use the with statement
to iterate over a file as you open it, the __exit__ method will remember to
close the file handles afterwards and x.close() is no longer needed.
*with open( “this.file” ) as x:*
* data = x.read)*
The line after *data* can be made to run further code per line and *data*will
be left as a list for you to manipulate once the iteration is done and
the file is closed.
*-------[ Thirdly { may want to avoid if new in python but gives more
control over operation }*
By utilizing streams and buffer pipes you get away with not defining a
file within your code but can make it read from stdin directly. i.e. on
the command line or within a shortcut launcher:
*myTool < myfile.txt*
You then need this inside your script, example shows a script that grabs
any line containing the word “*asset_token*” so when batched and ran in
paralell will extract all cases of that line from an entire server, sort of
like grep without the crazy flags to remember:
*import sys*
*parameter = “asset_token”*
*data = [ n for n in sys.stdin if parameter in n ]*
This method handles the file handle closing as your script exists as the
stream from stdin will be discontinued and your data container will be
there as *data *for further manipulation.
*---[ References*
http://effbot.org/zone/python-with-statement.htm
http://docs.python.org/2/tutorial/inputoutput.html
http://axialcorps.com/2013/09/27/dont-slurp-how-to-read-files-in-python/
http://codepad.org/Mq8YXBNf
Hope this stuff helps and you have fun with file handles!
p.s. by using os.path as in the example above rather than manually state a
path in string format you completely negate forward slash backward slash
issues, so to answer your pondering "*I don´t understand why I get \\\\ and
\\*" the answer is as simple as "*Because you are not using os.path*" :)
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