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For 2023 (and 2024 ...) - we are now fully retired from IT training.
We have made many, many friends over 25 years of teaching about Python, Tcl, Perl, PHP, Lua, Java, C and C++ - and MySQL, Linux and Solaris/SunOS too. Our training notes are now very much out of date, but due to upward compatability most of our examples remain operational and even relevant ad you are welcome to make us if them "as seen" and at your own risk.

Lisa and I (Graham) now live in what was our training centre in Melksham - happy to meet with former delegates here - but do check ahead before coming round. We are far from inactive - rather, enjoying the times that we are retired but still healthy enough in mind and body to be active!

I am also active in many other area and still look after a lot of web sites - you can find an index ((here))
Running an operating system command from your Python program - the new way with the subprocess module

Python's subprocess module has replaced a series of other modules, and if you're writing new code which calls operating system commands you should use this module in perferance to the older stuff. Easy examples at [here].

The "interesting bit" in various languages is not so much how you cal other commands and languages, but how you handle their inputs and outputs. Here are some subprocess examples:

Running a subprocess, output to file:

  stuff = open("demodata.txt","w")
  subprocess.Popen(["ls","-lat","/etc"],stdout=stuff)


Running a subprocess, output back to your Python script:

  proc = subprocess.Popen(["ls","-lat","/usr"],stdout=subprocess.PIPE)
  while True:
    record = proc.stdout.readline()
    if not record: break
    print record,
  proc.wait()


And you can handle stdin and stderr using exactly the same approach.

Older examples [here] and [here] (that latter showing polymorphism where you can read from a process or from a file in the same example!)
(written 2015-03-06, updated 2015-03-07)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
Y115 - Additional Python Facilities
  [183] The elegance of Python - (2005-01-19)
  [208] Examples - Gadfly, NI Number, and Tcl to C interface - (2005-02-10)
  [239] What and why for the epoch - (2005-03-08)
  [463] Splitting the difference - (2005-10-13)
  [663] Python to MySQL - (2006-03-31)
  [672] Keeping your regular expressions simple - (2006-04-05)
  [753] Python 3000 - the next generation - (2006-06-09)
  [901] Python - listing out the contents of all variables - (2006-10-21)
  [1043] Sending an email from Python - (2007-01-18)
  [1136] Buffering output - why it is done and issues raised in Tcl, Perl, Python and PHP - (2007-04-06)
  [1149] Turning objects into something you can store - Pickling (Python) - (2007-04-15)
  [1305] Regular expressions made easy - building from components - (2007-08-16)
  [1336] Ignore case in Regular Expression - (2007-09-08)
  [1337] A series of tyre damages - (2007-09-08)
  [1876] Python Regular Expressions - (2008-11-08)
  [2407] Testing code in Python - doctest, unittest and others - (2009-09-16)
  [2435] Serialization - storing and reloading objects - (2009-10-04)
  [2462] Python - how it saves on compile time - (2009-10-20)
  [2655] Python - what is going on around me? - (2010-02-28)
  [2721] Regular Expressions in Python - (2010-04-14)
  [2745] Connecting Python to sqlite and MySQL databases - (2010-04-28)
  [2746] Model - View - Controller demo, Sqlite - Python 3 - Qt4 - (2010-04-29)
  [2764] Python decorators - your own, staticmethod and classmethod - (2010-05-14)
  [2765] Running operating system commands from your Python program - (2010-05-14)
  [2786] Factory methods and SqLite in use in a Python teaching example - (2010-05-29)
  [2790] Joining a MySQL table from within a Python program - (2010-06-02)
  [3089] Python regular expressions - repeating, splitting, lookahead and lookbehind - (2010-12-17)
  [3442] A demonstration of how many Python facilities work together - (2011-09-16)
  [3469] Teaching dilemma - old tricks and techniques, or recent enhancements? - (2011-10-08)
  [4085] JSON from Python - first principles, easy example - (2013-05-13)
  [4211] Handling JSON in Python (and a csv, marshall and pickle comparison) - (2013-11-16)
  [4298] Python - an interesting application - (2014-09-18)
  [4439] Json is the new marshall, pickle and cPickle / Python - (2015-02-22)
  [4536] Json load from URL, recursive display, Python 3.4 - (2015-10-14)
  [4593] Command line parameter handling in Python via the argparse module - (2015-12-08)
  [4709] Some gems from Intermediate Python - (2016-10-30)

Y110 - Python - File Handling
  [114] Relative or absolute milkman - (2004-11-10)
  [1442] Reading a file multiple times - file pointers - (2007-11-23)
  [2011] Conversion of OSI grid references to Eastings and Northings - (2009-01-28)
  [2282] Checking robots.txt from Python - (2009-07-12)
  [2870] Old prices - what would the equivalent price have been in 1966? - (2010-07-14)
  [3083] Python - fresh examples from recent courses - (2010-12-11)
  [3465] How can I do an FTP transfer in Python? - (2011-10-05)
  [3558] Python or Lua - which should I use / learn? - (2011-12-21)
  [3764] Shell, Awk, Perl of Python? - (2012-06-14)
  [4438] Loving programming in Python - and ready to teach YOU how - (2015-02-22)
  [4663] Easy data to object mapping (csv and Python) - (2016-03-24)
  [4708] Scons - a build system in Python - building hello world - (2016-10-29)
  [4717] with in Python - examples of use, and of defining your own context - (2016-11-02)


Back to
Deciding whether to use parameters, conditional statements or subclasses
Previous and next
or
Horse's mouth home
Forward to
Binary data handling - Python and Perl
Some other Articles
Working out distance between places, using OS grid references and a program in Tcl
Everything is a string - even a list
Tcl variable names - no real limits!
Binary data handling - Python and Perl
Running an operating system command from your Python program - the new way with the subprocess module
Deciding whether to use parameters, conditional statements or subclasses
Spike solution, refactoring into encapsulated object methods - good design practise
What is the difference between a function and a method?
Overnight accommodation in Melksham - if Well House Manor is full!
Combining tests into suites, and suites into bigger suites - Python and unittest
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This is a page archived from The Horse's Mouth at http://www.wellho.net/horse/ - the diary and writings of Graham Ellis. Every attempt was made to provide current information at the time the page was written, but things do move forward in our business - new software releases, price changes, new techniques. Please check back via our main site for current courses, prices, versions, etc - any mention of a price in "The Horse's Mouth" cannot be taken as an offer to supply at that price.

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