Home Accessibility Courses Twitter The Mouth Facebook Resources Site Map About Us Contact
 
Python and Tcl - public course schedule [here]
Private courses on your site - see [here]
Please ask about maintenance training for Perl, PHP, Lua, etc
 
Python string formatting - the move from % to str.format

The % operator in Python has been a very clever and easy-to-use formatter, but has lacked the extensibility that's been incumbent on its structure and mirroring of the C sprintf function. Or - put another way - it was rather irritatingly running out of steam for some of the more complex formatting jobs, and users were having to write code and use modules to do whatshould really have been some fairly basic formatting.

At Python 2.6 the format method was added onto string object to provide a more flexible alternative, and as from Python 3 this will be / is the new standard.

The parentage of sprintf can still be seen in the new format method, although it's slighly longer to use.

Python 2.5:
  print "The value %.2f is the result" % val

Python 2.6:
  print "The value {0:.2f} is the result".format(val)

Python 2.7:
  print "The value {:.2f} is the result".format(val)
The position parameter 0 from 2.6 has become optional

Python 3.x:
  print ("The value {:.2f} is the result".format(val))
print is a function - as it always should have been - from Python 3.0

The string on which the fomat method is run is a template within which elements to be inserted are defined in curly braces. Each of these elements may comprise a number of parts - the main two of which specify what is to be inserted and how it is to be formatted. For example:

  val = 1000 / 7 ; # integer example
  print "The results is {0:4d} if you divide 1000 by 7".format(val)


uses the string {0:4d} to say "place the zeroth parameter to format - which is the value held in the val variable in my example - here. Output it to base 10 (decimal) and take up at least 4 character positions". There are a number of sensible defaults - the value will be right justified, left space filled if it doesn't need all the characer positions requested, for example.

With a formatter that's so flexible, you'll want to see plenty of examples and I have added an annotated program to show you a lot more - together with sample output - [here]. And we're moving over to using the String Formatter in new examples we write now that Python 2.5 and earlier is starting to get a little rarer. The "old stuff" still works so there's no need to go rushing to make changes to your existing codebase. In Python 3:

  val = 12.0 / 17.0
  print ("The value is %.3f - old style" % val)
  print ("The value is {:.3f} - new style".format(val))


Which runs as follows:

  wizard:oct11 graham$ python3 spy3.py
  The value is 0.706 - old style
  The value is 0.706 - new style
  wizard:oct11 graham$


As even .. "as taught on our Python Courses" ;-)
(written 2011-10-08)

 
Associated topics are indexed as below, or enter http://melksh.am/nnnn for individual articles
Y108 - Python - String Handling
  [4659] Prining a pound sign from Python AND running from the command line at the same time - (2016-03-03)
  [4595] Python formatting update - including named completions - (2015-12-10)
  [4593] Command line parameter handling in Python via the argparse module - (2015-12-08)
  [4360] Python - comparison of old and new string formatters - (2014-12-22)
  [4307] Identifying and clearing denial of service attacks on your Apache server - (2014-09-27)
  [4213] Formatting options in Python - (2013-11-16)
  [4152] Why are bus fares so high? - (2013-08-18)
  [4027] Collections in Python - list tuple dict and string. - (2013-03-04)
  [3886] Formatting output - why we need to, and first Python example - (2012-10-09)
  [3796] Backquote, backtic, str and repr in Python - conversion object to string - (2012-07-05)
  [3469] Teaching dilemma - old tricks and techniques, or recent enhancements? - (2011-10-08)
  [3349] Formatting output in Python through str.format - (2011-07-07)
  [3218] Matching a license plate or product code - Regular Expressions - (2011-03-28)
  [3090] Matching to a string - what if it matches in many possible ways? - (2010-12-17)
  [2814] Python - splitting and joining strings - (2010-06-16)
  [2780] Formatted Printing in Python - (2010-05-25)
  [2765] Running operating system commands from your Python program - (2010-05-14)
  [2721] Regular Expressions in Python - (2010-04-14)
  [2692] Flexible search and replace in Python - (2010-03-25)
  [2406] Pound Sign in Python Program - (2009-09-15)
  [2284] Strings as collections in Python - (2009-07-12)
  [1876] Python Regular Expressions - (2008-11-08)
  [1608] Underlining in Perl and Python - the x and * operator in use - (2008-04-12)
  [1517] Python - formatting objects - (2008-01-24)
  [1195] Regular Express Primer - (2007-05-20)
  [1110] Python - two different splits - (2007-03-15)
  [970] String duplication - x in Perl, * in Python and Ruby - (2006-12-07)
  [954] Splitting Pythons in Bradford - (2006-11-29)
  [943] Matching within multiline strings, and ignoring case in regular expressions - (2006-11-25)
  [903] Pieces of Python - (2006-10-23)
  [773] Breaking bread - (2006-06-22)
  [560] The fencepost problem - (2006-01-10)
  [496] Python printf - (2005-11-15)
  [463] Splitting the difference - (2005-10-13)
  [324] The backtick operator in Python and Perl - (2005-05-25)


Back to
Charities v Charitable. The cost of collecting your donation.
Previous and next
or
Horse's mouth home
Forward to
Teaching dilemma - old tricks and techniques, or recent enhancements?
Some other Articles
Static variables in functions - and better ways using objects
Vintage Bus Running Day in Warminster. An example of good bus practise.
Currently pictured in Melksham
Python string formatting - the move from % to str.format
Charities v Charitable. The cost of collecting your donation.
Passing of Steve Jobs - R.I.P.
How can I do an FTP transfer in Python?
Passing optional and named parameters to python methods
Busy weekend of contrasts.
4759 posts, page by page
Link to page ... 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96 at 50 posts per page


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.

Link to Ezine home page (for reading).
Link to Blogging home page (to add comments).

You can Add a comment or ranking to this page

© WELL HOUSE CONSULTANTS LTD., 2019: 404 The Spa • Melksham, Wiltshire • United Kingdom • SN12 6QL
PH: 01225 708225 • EMAIL: info@wellho.net • WEB: http://www.wellho.net • SKYPE: wellho

PAGE: http://www.wellho.net/mouth/3468_Pyt ... ormat.html • PAGE BUILT: Sat May 27 16:49:10 2017 • BUILD SYSTEM: WomanWithCat